First widefield attempt Orion complex

[pixueto]

Dear all,

I bought a cheap solignor 200mm 4.5F lense with a M45 adapter to try piggyback widefield AP on a budget. I focused to infinity, went a stop down (5.5) and attempted a series of 10 min subs with an LP CLS filter. Something went wrong but I'm inexperienced enough as to not having a clue about what the problem is. Not sure if focus was right (DSS wouldn't stack the subs) as I normally use a bahtinov for focusing but not this time. In this case I just moved the nozzle until it reached the infinite marking. I also took one of the subs and tried to work with it. When I tried to align the channels, the blue one desintegrated as you can see in the pictures. Can someone give me an idication about what may be going on? I'm a complete novice in this field.

Thank you very much as always for you support. I really appreciate it.

Pix

[Ags]

You have overexposed the blue channel. You need to use shorter exposures or a lower ISO. Also, you focus is not quite right - I always shoot test shots and zoom in on the stars to double check my focus.

You only have a few values for blue (because the blue values are squeezed up against he right side of the histogram) so when you stretch them the few values you have get separated like the teeth of a comb.

[pixueto]

You have overexposed the blue channel. You need to use shorter exposures or a lower ISO.

Thank you very much! Can you elaborate a bit more on that? Why the blue channel and no others? I used a CLS filter.

[Tinker1947]

I think its also out of focus,,,,,

[Ags]

The CLS filter blocks most red/orange/yellow, so that leaves the blue least dimmed. Can you set you camera to show you the RGB histogram?

[pixueto]

The CLS filter blocks most red/orange/yellow, so that leaves the blue least dimmed. Can you set you camera to show you the RGB histogram?

Yes, What should I look for in the histogram in the camera? It is stright to the right end of the screen.

Thanks for your help. It's very informative.

[pixueto]

Thank you guys. It's very nice of you. I'm getting an idea about how to fix the problem. Before talking to you I felt like not using the 200mm lens any more!

What do you think about cromatic aberration? Can it be determined from this sub? Just thinking about whether the lense is usable.

[Xplode]

The picture needs to be in focus to see how much CA there is.

If you struggle with bad weatcher try to tak a pic of something during the day that is white with a dark background.

[pixueto]

Thank you all. This thread has been really helpful. Other thing that is worrying me a bit is whether the lense can actually focus to infinity as I'm using a M42 adaptor. Say that I manage to focus to a building more than 200m away. Would I be able to focus to infinity then at night?

[Xplode]

I think you need to focus on something at least a kilometre away to be infinity

[pixueto]

Well, I tried to align the blue channel to the best of my ability in this one single shot (althought that channel got completely ripped apart). Did a bit of stretching and this is the result. Lots of vigneting as no flats were taken and this is a single sub. Also the Orion nebula core is burnt out as I did not take any short subs and did not integrate them in the picture but I'm pleased that I can see a hint of the flame and horsehead nebulae and the stars seem to come up with a lot of colour considering I'm using an unmodded camera. Am I right to think this is encouraging? Yes, I also have to solve my focusing issues with this new lense.

After all the adcice you have given me in this thread, I'm thinking about taking 5-7 mins subs next t ime insteado of 10mins and keep an eye on the histogram making sure it doesn't go to the very end of the screen.

What do you think?

Thank you all for showing me the way.

Pix

[Gina]

That's better I'm using 200mm M42 lenses with adapters and find I get focus about half way between infinity and 50ft - it's way out of focus at infinity. These are Vivitar f3.5 lenses and the cameras are 1100Ds with colour filter removed but with Ha clip filter in one and OIII clip filter in the other (dual camera WF DSO imaging rig).

Try focussing on a bright star using live view - I generally use Lyra. Focussing on these lenses is extremely critical. Don't give up - these old film SLR lenses can give very good results

[pixueto]

That's better I'm using 200mm M42 lenses with adapters and find I get focus about half way between infinity and 50ft - it's way out of focus at infinity. These are Vivitar f3.5 lenses and the cameras are 1100Ds with colour filter removed but with Ha clip filter in one and OIII clip filter in the other (dual camera WF DSO imaging rig).

Try focussing on a bright star using live view - I generally use Lyra. Focussing on these lenses is extremely critical. Don't give up - these old film SLR lenses can give very good results

Thanks Gina. It might be me being dumb but I'm finding it extremely difficult to determine whether I have perfect focus with that lens at night even with live view. The fact that I'm using a clip filter doesn't help either. I'm too used to my bahtinov in the main 8'' scope! All I normally worry about is to get round stars but I'm not used to recognize what a good focus is as the Bahtinov takes good care of it. I think I might make a Bahtinov for the 200mm lens at F5.5 aperture. What do you think? Will it be too small?

[Gina]

I'm thinking of making a focus mask - maybe just a Y mask.

[pixueto]

That's better I'm using 200mm M42 lenses with adapters and find I get focus about half way between infinity and 50ft - it's way out of focus at infinity. These are Vivitar f3.5 lenses and the cameras are 1100Ds with colour filter removed but with Ha clip filter in one and OIII clip filter in the other (dual camera WF DSO imaging rig).

Try focussing on a bright star using live view - I generally use Lyra. Focussing on these lenses is extremely critical. Don't give up - these old film SLR lenses can give very good results

The thing that worries me Gina is that I manage to get focus with distantish objects nearly at the very end; very close to the infinity marking and I fear the focus for AP might be beyond that point!

[davew]

There are a few things that influence where the point of focus is but I should think that if you've a reasonably good adapter you'll be ok.

Have a go at what Gina said. Make a Y mask. Very easy. If you want good focus you really must use either the stars or perhaps Jupiter. I would recommend Capella. Nice and bright and works well with a 200mm lens.

You won't know until you try. It's a thing that could be discussed all week but takes 5 minutes to do.

Good luck,

Dave.

[Quatermass]

Nice one pix I used a Y mask for some time but made a bahtinov mask for my ed80 it just has a slightly better focus defraction I find but once used a Y mask from a twig to get a wide field image of the trifid and the lagoon

Sent from my GT-S5670 using Tapatalk 2

[pixueto]

Yes QM, I remember that one. Well, I've made the Y masks now I only need a clear night to try it! By the way, I got focus with the Moon a while ago between clouds. The focus is a tiny bit before the infinity mark. Am I right to asume that the focus with a widefield 200mm lens is pretty much fixed? I'll scratch the point where it reaches focus in the lens if that's the case and that would save me some work!

[RAC]

Yes QM, I remember that one. Well, I've made the Y masks now I only need a clear night to try it! By the way, I got focus with the Moon a while ago between clouds. The focus is a tiny bit before the infinity mark. Am I right to asume that the focus with a widefield 200mm lens is pretty much fixed? I'll scratch the point where it reaches focus in the lens if that's the case and that would save me some work!

Focus on a lens can't just be marked, it is far too sensitive for that. Its a waste of time to do heaps of subs and only to find you have wasted the clear night. I made a bahtinov mask for my 400L lens and even check it halfway through imaging as i find it shifts a bit in the first hour.

[Gina]

Focus on a lens can't just be marked, it is far too sensitive for that. Its a waste of time to do heaps of subs and only to find you have wasted the clear night. I made a bahtinov mask for my 400L lens and even check it halfway through imaging as i find it shifts a bit in the first hour.

I've found focus is extremely sensitive with my 200mm lenses and am going for full remote control from the warm room, where I can sit right in front of the monitor and adjust focus. I've tried various methods of manual control including a knurled nut on a screw but even that is too sensitive. Interesting that you find focus changes on your 400mm lens - I'll have to watch out for that. I'm going to make a focussing mask - I'll try a Y mask first and see how well that works. I've done a few hours subs with the 200mm but focus was a bit off - I need to fix that.

[Quatermass]

Thats a good point about checking focus. I use backyardeos and check focus halfway through my set of subs it often slips out of focus a tiny amount on a long run.

Sent from my GT-S5670 using Tapatalk 2

[pixueto]

Well, the weather is not helping lately to do some AP so I decided to make a bahtinov mask for the 200mm soligor 4.5 lens. I found an interesting site about a project for a bahtinov using strings: http://njstargazer.org/Bahtinov.asp

I thought, why not doing something similar for a mask with a 36mm aperture? After all, I was having trouble cuting the tiny slots given by the mask generator at: http://astrojargon.net/MaskGen.aspx

So what I did is to use sewing thread instead of nylon for the tiny bahtinov for my 200mm lens. You can see the result in the picture. I've used cardboard, sewing thread, a needle and sellotape. The printer run out of black ink, by the way. I'm yet to try it so we'll see if it works. Somehow I didn't manage to have all the threads parallel but, after reading an excellent tutorial on difraction spikes I don't think that really matters. Time will tell. I can't wait to try it and see.

[Gina]

Very interesting I want to make a focussing mask for my 200mm lens so I'll be very interested in how well yours goes.

[pixueto]

It appears that I'll be able to try it tonight. It's a bit windy and the moon will be out any moment now but I don't think I'll get another chance for a while.

[pixueto]

Well, I'm happy to report that the mask with the sewing threads works brilliantly. Gina, you were right; real focus is way, way out of the infinity mark. I've got the camera outside taking widefield pictures of the Andromeda galaxy but when I'm done with that I'll upload the pictures with the makeshift bahtinov so you can see how good they are. By the way, that's my five year old holding the focusing mask (in case you guys wondered how big the mask is for a 200mm lens -or how unwrinkled my hand was for an old fogy!)

Still havin trouble with my subs; anything more than 5min subs and the blue channel disappears out of the right side of the histogram. I would have expected to be able to take longer subs with this setup. I wonder why the 200P didn't give me problems with that and now I seem so limited. Is it the lens perhaps?