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Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

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  #1  
Old 12-08-2010, 11:55 AM
Martin Pugh
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Moving into widefield astrophotography

Hello everyone
best place I thought to pose this question would be in IIS given the amount of very talented DSLR users.

I am going to buy the 90mm Solarmax II scope (once Meade ships), and while I look forward to observing with this, I will certainly want to take photos.
Now - I also have a very nice f6.6 500mm Borg 76ED scope, which is redundant, and can be reduced to 430mm/f5. The reducer is designed for DSLRs.

Of course - I dont quite yet understand how I will attach a camera to the Solarmax, but I want to be able to use the camera interchangeably between solar and deep-sky/widefield imaging.

Been looking at a lot web sites - what would make the Canon 550D at just $880 a bad choice? Afterall, it seems to have all of the same capabilities, except perhaps it is not modded to be more sensitive at 656nm. It also has very nice 4.3micron pixels.

My other thoughts were the ST8300 OSC - makes things nice and light, and its cooled.

Grateful for some suggestions.

cheers
Martin
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  #2  
Old 12-08-2010, 01:38 PM
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renormalised (Carl)
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Even though it is quite a bit dearer, I'd go for the OSC. Why, because it has a better dynamic range spectrum wise, better QE, far less hot pixels, less dark current, higher full well and it's already cooled. Pixels aren't as small as the DSLR's but you'll be able to use it on a wider range of scopes than the DSLR because of that. One good thing about the DSLR....you can run it off batteries. The ST needs a power supply, which means extra cables/cords to deal with.

To be very useful for solar observing, you'll have to mod the 550D so it can pick up the Ha from the Sun, which means extra money spent and more time wasted waiting for it to be modded.

Mind you, 18 megs a pickle versus 8.3, it's a bit of a choice!!!.
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  #3  
Old 12-08-2010, 04:47 PM
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seeker372011 (Narayan)
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umm i dont think you need a modded dslr to image through a narrow band telescope
But i dont see many people doing that,the dmk or similar seems to be the preferred instrument ...large number of frames etc

Dont know if you can get a full disc even with a dslr?
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  #4  
Old 13-08-2010, 08:52 AM
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Martin,

Monochrome for the solar scope. Colour is useless through one of these scopes. You really need something like a 41DMK or one of the smaller SBIG, FLI or QSI cameras.

For the Borg, why not stick with monochrome and filters? If it is easy of use then a OSC is going to be better overall than a DSLR. However, there is some really nice work being done with a DSLR, but it would need modding and cooling.

Hope that helps.
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  #5  
Old 13-08-2010, 09:24 AM
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What do you define as wide field Martin? Three degrees? Seven degrees or far higher?

I have been battling with all the various parameters for years to get decent resolution wide fields.

The combination of big sensor with shorter FL very high quality optic. This leads to vignetting and CA and astigmatism due to off axis aberrations. We are trying to beat the laws of Physics here and will not ever win. This can only be overcome by careful processing and control by fine tuning of the light that actually enters the system.

Very short focal length optic will limit the resolution.

There is no easy answer.

All the methods I have worked out for wide fields where the stars are inherently undersampled seem to be getting somewhere.

If the weather permits will apply these methods to data at about 90mm FL and see what happens.

Welcome to the matrix! Take the blue (OSC) or the red (Mono) sensor?

Bert
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  #6  
Old 13-08-2010, 01:11 PM
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philiphart (Phil Hart)
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hey martin

sounds like fun!

for the solar stuff, i'll defer to the high-res imaging experts, but i assume that you'd get higher res results from a video solution rather than DSLR but i you trade that against a much wider field of view with the DSLR. not sure if the large format video mode on the DSLR is sensitive enough for that kind of work but it would sure result in a lot of data!

for the widefield stuff, the biggest consideration is probably whether you plan to use this mainly at a powered/permanent site or whether you want it to be easily portable and quick to setup and run when you're away camping somewhere. if the former, then i would also lean towards OSC CCD. if the latter, then DSLR has some more appeal.

of course the small pixels are attractive for the high res solar work, but less so for SNR characteristics on the faint fuzzies. will be interested to follow your choice and hear how it goes.

Phil
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  #7  
Old 15-08-2010, 09:58 PM
ptc (Richard)
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Quote:
Originally Posted by Martin Pugh View Post

My other thoughts were the ST8300 OSC - makes things nice and light, and its cooled.

Grateful for some suggestions.

cheers
Martin
why not use your standard imaging camera with medium format camera lenses like the pentax 6x7?

they work great for me and the lenses are widely available on the used market. you can use the largest or smallest sensors and have plenty of back focus to use a camera + filter wheel + inline focuser such as the PDF

here are some recent examples

PL39000M
http://www.narrowbandimaging.com/ngc...2hao2_page.htm

http://www.narrowbandimaging.com/ant...r_rgb_page.htm

PL39000C (one shot color) includes photo of imaging system
http://www.narrowbandimaging.com/gam...pl39k_page.htm

ML8300
http://www.narrowbandimaging.com/ngc...Ha_o3_page.htm

http://www.narrowbandimaging.com/hor...gb_ha_page.htm

hardware:

http://www.narrowbandimaging.com/mou...m_cla_page.htm

http://www.narrowbandimaging.com/mar...ystem_page.htm

other examples of images

http://www.narrowbandimaging.com/widefield_page.htm

One shot color is OK but it always gives poorer results than color sequential unless you downsample after processing. I did it for a year and concluded that the monochrome always gave better results

I have plenty of ONE shot Color images from 2009 on my website under the "latest images" tab that has everything in reverse chronology

best regards
Richard
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  #8  
Old 16-08-2010, 09:34 AM
Martin Pugh
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Thanks everybody for the replies -I knew I would get sensible answers here.

I hear all the pros and cons, and I think I will drop the idea of an OSC.

Paul - why do you say the DSLRs are useless for solar imaging? I say that having never hooked up a DSLR to a solar scope but in theory, I can see great detail on the surface of the sun, or I can tune it to focus in on prominences. So, the latest DSLRs have full HD video capability. So, why would I not be abe to capture the same view to 30fps HD video via the DSLR? That's the theory any way, but as I say, never done it and I have a while to wait before the solar scope arrives.

Bert - I dont think I am looking to substitute my regular FSQ/STX combination for widefield stuff....that is already 4degs x 4degs, but simply to add to imaging options for very wide field - you know, wide area shots to capture meteorites or large asterims etc.

I will let you all know what I opt for and post results!

cheers
Martin
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  #9  
Old 16-08-2010, 01:14 PM
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Martin, my reasons are as follows:

1. Hydrogen alpha views of the sun are full monochrome and using a DSLR cannot possibly show all the detail or image quality that monochrome can.

2. When I used a DSLR as a try out the image was totally red and very dark, no matter how much ISO I applied. It contained little detail too.

3. Trying to process this out is very difficult to say the least, and I was not successful.

4. All the great images in Ha Solar come from monochrome cameras.

Still you could try with the HD DSLR.
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  #10  
Old 16-08-2010, 02:47 PM
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[1ponders] (Paul)
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I'll second Paul's comment re DSLR. Why go for 1/4 resolution (BGGR Baayer matrix, with nothing showing through the B and G, though you might get some leakage across the wells, happens with some cameras) when with a monochrome camera you can make every pixel count.
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  #11  
Old 16-08-2010, 10:05 PM
chunky (Clinton Wood)
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DSLR for solar

My 2c worth.

I remember a guy from Holland (PM Heden), that you could look up - some incredible solar shots from a DSLR.

http://www.clearskies.se/Gallery%20Deepsky.htm

Ciao
Clinton
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  #12  
Old 17-08-2010, 11:24 AM
Martin Pugh
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Thanks Paul for the additional comments.

Clintn - thanks for the link...great stuff on that site.

cheers
Martin
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  #13  
Old 16-10-2010, 11:23 AM
Martin Pugh
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Hello everyone
I said I would come back and let you know what I opted for.
I bought the new Canon T2i Rebel (550D), and sent it off to Hap Griffin straight away to have it modded while I worked through the manual.

I then did a lot of reading about lenses and opted for a fixed FL, the 85mm f1.8 USM lens.

I received that yesterday, and mounted the camera next to my FSQ and off I went.

I have to say I am shockingly disappointed. The first images (60 secs, ISO 800) were just terrible. Huge coma. I also thought I had achieved a good focus, but the images were dreadfully out of focus, suggesting th lens focus position moved during a slew.

I stopped the lens down 2 stops to f2.2, to no avail. So I will try f4 next.

I thought the fixed focal length lens were supposed to be far superior to telephoto lens. I also understand this is an APS-C format camera, so it physically isnt full 35mm frame format, like the 1D etc.

So, right now, very disappointed.

tips anyone?

cheers
Martin
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  #14  
Old 16-10-2010, 01:21 PM
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Octane (Humayun)
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Martin,

The 85mm f/1.8 USM is an excellent portrait photography lens, however, it's not designed for astrophotography.

The longer focal length L-series lenses such as the 200mm f/2.8L II USM, or 300m f/2.8L IS USM, and even the 300mm f/4L USM are better suited to flat fields.

And, yes, you must stop down these lenses, unless you wish to use an external aperture mask -- the benefit of the external mask is that it prevents diffraction spikes caused by lens diaphragm.

Here's a field that I did with the 200mm f/2.8L II USM on my old 40D (now sold; same sensor size as your 550D): http://members.optusnet.com.au/mrozy...elt_Orion.html

H
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  #15  
Old 17-10-2010, 07:45 PM
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philiphart (Phil Hart)
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I'm a little surprised by your experience Martin.. I would have thought that lens would be up to the job (but I've never tried it).

Here's a few thoughts..

With my 24mm f1.4, 50mm f1.4 and 200mm f2.8 lenses, I image at about f3.5. I don't expect to produce sharp stars at f2.2 with any lens (and technically, going from f1.8 to f2.2 is not quite even one stop?). Certainly in my experience, the fixed focal length lenses are better than zoom lenses but I've never used the 85mm.

The only recent lens I've ever had trouble with was a 50mm f1.8 lens which must have got knocked or something and had a tilted lens element so displayed different focus across the frame. I would guess that you would have noticed if the image quality was different across the frame rather than just the same coma in all corners?

I assume you have liveview focus on that camera? Once you've slewed to the scene you want to shoot, you should have a star bright enough to liveview on and focus there. But slewing shouldn't be enough to change focus unless something like a dew heater strap is causing it.

Maybe you can borrow a lens to try something different. A lot of places hire Canon gear.. perhaps you could try that if nobody near you has one you can try?

Phil
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  #16  
Old 17-10-2010, 08:06 PM
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dugnsuz (Doug)
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Quote:
Originally Posted by Martin Pugh View Post
Hello everyone
I said I would come back and let you know what I opted for.
I bought the new Canon T2i Rebel (550D), and sent it off to Hap Griffin straight away to have it modded while I worked through the manual.

I then did a lot of reading about lenses and opted for a fixed FL, the 85mm f1.8 USM lens.

I received that yesterday, and mounted the camera next to my FSQ and off I went.

I have to say I am shockingly disappointed. The first images (60 secs, ISO 800) were just terrible. Huge coma. I also thought I had achieved a good focus, but the images were dreadfully out of focus, suggesting th lens focus position moved during a slew.

I stopped the lens down 2 stops to f2.2, to no avail. So I will try f4 next.

I thought the fixed focal length lens were supposed to be far superior to telephoto lens. I also understand this is an APS-C format camera, so it physically isnt full 35mm frame format, like the 1D etc.

So, right now, very disappointed.

tips anyone?

cheers
Martin
Hi Martin,
I'm having the same feelings towards my 24-70mm f2.8L lens - great for daytime, woeful under the stars...but I knew that on the way into the purchase so there's no excuses really - like H said, great portrait lens.
My other lens is another story altogether - contrary to the primes are better than zooms argument, the 70-200mm f4L IS is working out very well in the dark - Flat field, nice colour correction.
Here's my initial test...
http://s327.photobucket.com/albums/k...current=19.jpg
Check out the MTF scores then compare the zoom range with its equivalent L primes...
http://www.photozone.de/canon-eos/19...review?start=1
And last, compare the 70-200 @85mm f4 with your 85mm prime @f4...
http://www.the-digital-picture.com/R...mp=0&APIComp=5

All is not lost Martin
Sell the 85 and get a 70-200 f4L IS!!

All the best
Doug
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  #17  
Old 17-10-2010, 08:24 PM
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h0ughy (David)
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Quote:
Originally Posted by Martin Pugh View Post
Hello everyone
I said I would come back and let you know what I opted for.
I bought the new Canon T2i Rebel (550D), and sent it off to Hap Griffin straight away to have it modded while I worked through the manual.

I then did a lot of reading about lenses and opted for a fixed FL, the 85mm f1.8 USM lens.

I received that yesterday, and mounted the camera next to my FSQ and off I went.

I have to say I am shockingly disappointed. The first images (60 secs, ISO 800) were just terrible. Huge coma. I also thought I had achieved a good focus, but the images were dreadfully out of focus, suggesting th lens focus position moved during a slew.

I stopped the lens down 2 stops to f2.2, to no avail. So I will try f4 next.

I thought the fixed focal length lens were supposed to be far superior to telephoto lens. I also understand this is an APS-C format camera, so it physically isnt full 35mm frame format, like the 1D etc.

So, right now, very disappointed.

tips anyone?

cheers
Martin
do you have a few of the shots to show. dew straps are a bugger at times because as you slew they move the focus - many a time has this happened. It could well be that the mod you had done was not placed back in the right position? when you use autofocus is it sharp - it may need adjustment? i use a bhatnov focus mask - which works very well with the live view
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  #18  
Old 18-10-2010, 05:44 AM
Martin Pugh
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Thanks for the additional comments there. Useful indeed, since I did have a heater belt on it. I will remove it next time out.

I kind of expected things not to be perfect of course, but the results were just rubbish.

While the 85mm might be a great portrait image, I cant understand why it would not be good for astrophotography given the MTF curves.

Doug - I did see your initial tests before I bought the 85mm, and almost opted for that same lens, but I wanted to keep the cost down a little, as this is not my main line of astrophotograhy. So, the 85mm lens, with the reviews it had, was just $386.

I do not use Liveview for focussing. I connect to the camera from within Maxim, draw a crop around a bright star, and then take continuous 1 second images using the "View Large Statistics" menu item. I continue to focus until I reach the lowest achievable FWHM I can. Of course, doing this by hand is not perfect either.

I assume that to stop these lenses down, you can only do it via software or external aperture mask. I do not see any physical adjustment on the lens itself.

I will take some daytime shots with the 85mm lens and post them for comment, then I will stop the lens down some more and post some nightime shots also for you DSLR experts to analyse.

thanks for the links and help

appreciate it very much.

Martin
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  #19  
Old 18-10-2010, 06:47 AM
gbeal
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Martin,
while everyone will have their favourites, I have had good results with a couple. My first was the Leica R series 180/4, stunningly sharp, and well made. Well priced too.
Where it failed was the back-focus side, as the CCD and CFW added up to more than the distance from the rear flange to chip. Yes I could have possibly worked something, but the easier option was to go to Plan B.
Plan B was a couple of Pentax 67 lenses, currently a 200/4, and a 55/4. Both have as you would expect gobs of back-focus, and are sharp as I feel I need. Bonus here is they are well priced too.
Gary
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  #20  
Old 18-10-2010, 07:28 AM
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dugnsuz (Doug)
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Martin - sorry misread your post. Thought you had bought the L version of the 85mm lens.
Doug
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