Orion nebua and Double cluster.

[ajohnw]

I already have some photogear Haseeb. Bought with my megrez 110mm. Given the lights round here now I will probably wish I had used it when I bought it. It's the usual thing. 50mm extension, 2in fitting, filter thread at one end and T at the other. When a filter is fitted dust can't get in. If this one is too long shorter ones are available.

The passband of the OVL filter is different to the CLS ones that are available

OVL UHC



Astronomik CLS II


The OVL is similar with one half missing. More honest as well because they never transmit 100%. There are a number of similar ones to the Astronomik around. It would have been great when we had low pressure sodium lights around. The only source of problems then but I think the rejection filter was a better idea for curing that as it let everything else through. As far as I know they were only sold and made in the UK. Urban observatories use them but I have no idea where they get them from. They didn't need to block much light or many colours as this shows.



This is what I think they are using now. Lights higher, more powerful and yet more of them.



I read a paper by the IEEE on this subject. There is a chance that they are low cri LED lamps. It seems these can compete or at least get close to the efficiency of low pressure sodium. Low cri because they emit a lot less blue. Another reason for choosing a filter that passes more at that end.

If I'm having a bad day I might even build a cd based spectrometer and see what they actually give out. We really need black out curtains in front bedrooms now.


John
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[HaseebM]

I think both those filters are good John and have their own merits, one being good for Hydrogen alpha and another, i.e., CLS II for reflecting nebulae. I have not used the UHC's but the CLS II does help in bringing out colour in reflecting nebulae and I find using it on objects such as Lagoon nebula a real treat. Here's one I shot with this filter on. Only source of issue being, trying to get rid of the 'blue hue' with CLS.

[ajohnw]

Maybe the answer is to just do B&W.

The other one I wondered about getting looks pretty similar to the Astronomik. The Baader UHC-S. That should looks something like this.



Baader also do a moon and skyglow with IR cut but it looks like it's just intended to severely cut low pressure sodium lighting and let the rest through.

I bought the most severe to see what it does with the street lights. If nothing their UHC-S doesn't stand a chance so maybe one of those next. They can always be sold on ebay - as new, just opened. Helps keep the cost of finding out down. The main interest with these really is use in the back garden.

I should be ordering the mount next weekend. I'm away from home most of next week some one will be in but I would rather be around when it arrives.

John
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[NorthernFocus]

That's awesome. Proof positive that photography has endless possibilities.

[ajohnw]

That's awesome. Proof positive that photography has endless possibilities.

You may live in one of the more ideal locations Dan and have darker skies nearby. I reckon a good guide is how much of the milky way can be seen visually. The ideal situation is from horizon to horizon but directly overhead isn't too bad. The bigger the arc the better. I've never been able to see it where I currently live but while low pressure sodium lighting was used a simple filter improved things dramatically. Still limitations visually but cameras change all of that as they can capture light for long periods so are way more sensitive than our eyes. They have revolutionised astro photography. A lot can be done with camera lenses. Camera platforms can be bought but when I look at how they are set up I have to wonder. One for instance is fitted with a ball head to point the camera where needed and the suggestion is to mount it on a Manfrotto geared head and then on a decent tripod. It will track ok but I would seriously wonder about alignment with the geared head. I feel a real equatorial mount like the one I am going to buy is a much better option and costs compared with platform, geared head and tripod aren't all that much different. The weight will be higher than a camera platform set up but a company has decided to make a decent relatively lightweight mount.

Telescopes benefit from being small for use with a dslr. The reason is field of view on various sizes of sensor. Taking the one I have just bought an 80mm F7.5 used with a flattener the F ratio comes down to F6 and I can get the Andromeda galaxy in on a full frame camera. It's about 3 degrees across and the sensor would cover 4.3 degrees. It would cover 2.8 degrees on a crop camera. A 70mm F6 telescope would cover 4 degrees with a flattener on crop as the focal length is shorter. That sets the image scale. The flattener is needed because typical refracting telescopes produce a curved focal surface so using one helps keep stars round out to the edge of the frame. I've just tidied up an old spread sheet to include this sort of thing. Also to see how my eyepieces work out with the scope. F7.5 helps in that area as it doesn't need complicated eyepieces. The usual F6 isn't too bad in that respect but probably deserving of a bit more expense in that area.

Visual use is different. Size sets how much light they capture and the telescope's resolution but on the other hand resolution is often limited by the atmosphere and big scopes take some time to settle down optically. Extra size means dimmer stars can be seen but cameras take care of that aspect. Bigger sizes show more detail on planets and the moon if conditions allow. Often at say 250mm which I have used the scope might take an hour to settle down providing it was put out after the sun had gone down but seeing conditions could still limit what can actually been seen. A famous older book reckoned 200mm was a sensible limit for most people who take a scope out of the house to use. Taking the total weight of the gear and other factors into account I would be inclined to agree. Bigger scope can be used at higher magnifications. That means the weight of the mount tends to increase dramatically as size goes up. As things stand manufacturers try but if it's portable even with a struggle things bounce around as soon as the scope is touched. Be interesting to see how the one I am buying works out. They reckon the payload can be greater than the stand itself. I'm attracted by the payload it can take even if it all wobbles about too much. The payload suggests it's a lot more generally robust than other stands of a similar weight. Also hopefully far more precise generally.

John
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[NorthernFocus]

Thanks for all of the information, John. Around Anchorage we have a good bit of light pollution. But it's true one doesn't have to go far to get away from it. Interior Alaska is better for observing the heavens. More clear nights. But darn cold. And when it's not cold there is really a LOT of light pollution

[HaseebM]

From where I live, light pollution is a huge problem and increasing. Even then you get used to it once the interest ignites and you say many things which could be considered a no, no from such LP conditions. I started with a 8" Dobsonian and now even with a 71mm WO, I can see some of those objects. Planets are no problem as sometimes LP can help with brighter Planets like Jupiter and Mars for instance. Only issue I don't seem to have is thermal equilibrium, perhaps due to my hot, humid conditions wherein it does not take much time for the scope or there is hardly noticeable drop in temperatures. Irrespective I allow the scope to cool-down and use this time to align the mount.

Alaska must be a great place to watch the heavens but dew could be an issue. Refractors are great and hardly require cooldown times and most of them if not all, come with dew shields.

[ajohnw]

Actually going on Sweden not far from the artic circle cold helps in other ways - gets rid of the moisture in the air. I used to go there for a couple of weeks usually end of Feb when the bulk of the snow had fallen. Dressed for Everest expeditions -20C or worse was ok providing I remembered to breath through my nose. Not sure I would use a telescope in that but I could be tempted down to -10 or so. I have stood / sat by a hole in the ice fishing in temperatures like that for hours - usually in the sun as the weather is generally good that time of year.

No - thought it might be worth posting a little as people are reading the thread and might get tempted. It's much easier to buy entirely the wrong gear compared with cameras.

John
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[ajohnw]

Dew is a big problem in the UK Haseeb. Best times for viewing is usually winter and around that time. There is plenty of moisture in the air so the telescope radiates heat into outer space when the skies are clear and as it's metal quickly gets below the dew point. I've had the eyepiece end of a refractor get soaking wet. The part that camera people would call a lens hood seems to have saved the optics so far but some people fit heaters. Odd thing to do really has heat from a building can spoil seeing when high magnifications are used. Patios that have been in the sun all day have been reckoned to do the same thing as well. I suspect this mostly relates to people who are using very superior optics where the magnification can really be pushed up. Something that actually is difficult to buy. Pentax did make a refractor that claimed to be diffraction limited right to the edge of the field. The add changed suddenly. Telescope specs are not usually that specific. Some types of telescope can have very high levels of optical quality but only on axis with very limited fields of view. Just what is needed for high magnification.

John
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[HaseebM]

As an aside, I have a friend by the name of Jaspal Chaddha who lives in London. He continously takes images which are astounding to say the least right from where he lives. His images have also made it to some of the major Astronomy magazines in U.K., including NASA. You should check him out if possible through local directory, I am sure he will be willing to share his knowledge. He has his own observatory so perhaps keeping control of dew?

[wrench]

I just wanted to say that these shots are amazing.

[ajohnw]

As an aside, I have a friend by the name of Jaspal Chaddha who lives in London. He continously takes images which are astounding to say the least right from where he lives. His images have also made it to some of the major Astronomy magazines in U.K., including NASA. You should check him out if possible through local directory, I am sure he will be willing to share his knowledge. He has his own observatory so perhaps keeping control of dew?

He has a web site and a flickr page. When I first saw the shots I thought he was using several narrow band filters. Usually 3 from comments on the flickr pages.

http://www.jkobservatory.net/

https://www.flickr.com/photos/95267225@N06/

The b&w ccd camera he uses isn't that large which is interesting, costs from $3500 !!!! though. One of his images has found it's way to the telescope he used manufacturers site.

https://www.altairastro.com/product.php?productid=16735

John
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[HaseebM]

We share a page on Flickr by the name Au ( Astronomers United ).

[ajohnw]

As this thread has touched on filters several are compared here

http://www.astrosurf.com/buil/filters/curves.htm#LIGHT POLLUTION REJECTION POWER

Astronomik are generally sharper but if there is nothing causing problems in the wider ones ??????????

Lumicron also have a pdf on their site with a guide to their filters. It even suggests exit pupils to use with them - effectively magnification related to the size of the optics. Certain exit pupil sizes suite specific purposes. For the same exit pupil magnifications gets greater as the scope increases in diameter so the data is of use on any scope. Only of interest for visual use really.

John
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[HaseebM]

Though I do not use filters of any kind for visual use, I do know in general astronomers prefer Lumicon. For a more in-depth read on the use of filters, google David Knisely who has written an article comparing various filters.

[JBW]

The B&W M42 is close to what I can see on a good night in my 8". Is there some way to not have such a bright center area?

[HaseebM]

The B&W M42 is close to what I can see on a good night in my 8". Is there some way to not have such a bright center area?

Indeed there is. You need to take separate 15 - 25 sec exposures and merge them with the main image so as not to overexpose the core.

[ajohnw]

There are some results from slightly different exposures here. The pages look to be a useful reference. Images available for DIY too.

http://www.rawastrodata.com/nebulae.html

In terms of HDR through a telescope I'd guess it will be like a microscope. Good at showing a cameras lack of dynamic range compared with an eyeball view. Must admit I have not tried a 14bit a/d yet though.

I didn't have much choice about using filters visually. No chance of seeing a number of things especially nebulosity. The light loss from just rejecting low pressure sodium lighting was minimal. It's probably going to be too great rejecting what's around now which means trying to photograph things that can't be seen visually through the scope.

John
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[ajohnw]

The OVL filter clears up the orange rather well and makes some forms of lighting in houses opposite look a rather weird green. Car headlamps get a blue tint. The remaining light levels may be from the moon, not sure.

Feeling manic I have found a fold up paper spectroscope kit that can read to 5nm so feel I just have to look into this further. I'll probably find that the light levels need to be high but can't resist trying. I added a 100mm fresnel lens to the order to stand a chance of intensifying it rather than trying to fix it on the end of a camera lens or telescope.

John
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[HaseebM]

Let us know how it goes. I wouldn't worry about intensifying the light for long exposures.