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digital_davem

Photographer new to astronomy needs help fixing cameras to focuser!

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Hi folks

Complete newbie astronomer but experienced photographer...

I recently acquired a classic 1970s long tube Prinz 660 3" refractor (1250mm/f16).  It came as part of a boxed set with 0.956" accessories but no tripod and an incomplete EQ mount (just parts).   I've been refurbishing it for a few weeks and it now has a 1.25" visual back, diagonal, red dot finder and a couple of modern low cost plossls and is fitted with tube rings and an arca-swiss plate and mounted on a manfrotto 055c tripod and pan/tilt head. The tripod is just adequate for visual work if you are careful.  Eventually, I intend to get a dedicated astronomical mount (maybe a skytee or an EQ5). For now, I'll make do with the camera tripod (which I'm going to try and strengthen).

I've just finished getting the thing set up for proper use and tonight I had my first real go with it (an hour moon viewing). Everything worked as expected thankfully. I even tried getting some snaps and a bit of video with my camera held up to the eyepiece (no lens attached). It kinda worked but a bit iffy! 

I know that there are various adaptors available (eg from ebay) that allow a camera to be mounted directly on the focuser without an eyepiece. Presumably in this configuration, the scope acts like a 1250mm/f16 telephoto lens.  I appreciate with my mount and tripod, nothing very ambitious is possible.

There appear to be a whole variety of different adaptors on offer that look quite different.  Some are very short 1.25" to T-mount adaptors, some are much longer, some have adjustable length tubes. One even combines a camera connector with an EP diagonal so you can switch between visual and imaging by turning a knob and one even has a built in eyepiece!

 I have 4 suitable cameras available (all 16MP):  a Sony NEX 5n,  a Fuji XA-1, a Fuji XE-1 (all APS-C) and a Panasonic Lumix G6 (m4/3). I also have quite a selection of cheap chinese lens adaptors that allow various brands of lens mount to work on these cameras. 

Any thoughts on what is the most suitable (and cheapest!) way to mount the cameras?

Thanks

Dave

Links to various ebay scope-camera adaptors:

http://www.ebay.co.uk/itm/Telescope-1-25-eyepiece-connection-for-Nikon-DSLR-Camera-Photography-Flip-Mirror-/261344855554?hash=item3cd95e0602:g:jD8AAOxyTjNSnEPb

http://www.ebay.co.uk/itm/1-25-Variable-Projection-Camera-Adapter-Telescope-for-Canon-DSLR-Camera-New-/261344896846?hash=item3cd95ea74e:g:RAQAAOxy3zNSnFm1

http://www.ebay.co.uk/itm/1-25-Telescope-Mount-T-T2-Lens-Adapter-for-Sony-DSLR-Camera-A58-A65-A77-DC617-/311490063116?hash=item4886412b0c:g:iNMAAOSwnipWUMpH

http://www.ebay.co.uk/itm/1-25-26mm-Telescope-Eyepiece-Adapter-for-Canon-EOS-EF-EF-s-mount-DSLR-cameras-/321179886039?hash=item4ac7d021d7:g:-8YAAMXQxU5R~-Ev

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If you have adapted the telescope to 1.25", then any 1.25" to T mount and an appropriate T-ring adaptor for your camera will allow it to connect.

What is not at all certain is weather it will come to focus, and weather the mount will keep it steady enough to get a decent shot of the moon. 1250mm on an APS-C chip will just about fit the moon in. I am afraid you will struggle to get a picture of anything else with it. 1250mm isn't anywhere near long enough for photographing planets and f/16 is way too slow for anything deep sky. Added to that, for astrophotography, the mount is the most important part of the equipment. It needs to be rock solid. Sorry to sound so negative but being an experienced photographer is probably a handicap when it comes to astrophotography.

Take some time to read around our imaging sections and you will get a feel for the equipment and techniques that are needed.

Don't let any of this put you off though. Even a shot of the moon is a great introduction to astrophotography. Give it a try :)

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With the equipment you currently have, prime focus imaging would be the most viable but as Rik says, you will be rather limited to Lunar images but that is a great introduction to astrophotography. For prime focus imaging, a simple 1.25" to 'T' adaptor will be required but you may very well require an extension tube to achieve focus.

Download a free piece of software called Registax, capture 25 or more images of the Moon and combine them using Registax and you may well be delighted with the results but deep sky objects will be beyond your reach from an imaging point of view.

Sent from my iPhone from somewhere dark .....

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Thanks!

What is the likely focusing problem with this arrangement? My scope is a refractor with a fairly long draw tube. Is the problem that the draw tube reach might be too long or too short?

Regarding potential targets, the moon is the obvious one but what about saturn and jupiter? Admittedly, the moon is the only thing I've actually looked at with my scope so far but let's put that inexperience to one side!  Using my m4/3 camera with its 2x "crop factor",  I'll have 50x magnification effectively. With a 2x teleconverter on the camera that could be 100x.  I guess the problem is not so much magnification but brightness?

I did a little experiment the other day, imaging the Pleides. Using my 300mm telephoto with a 2x teleconverter and the m4/3 camera (effective focal length 1200mm, similar to the native FL of my scope) I did manage to get recognisable shots of the cluster. The problem was that exposures greater than about 1/10th of a second showed either star trails or simply tripod wobble (elongated stars).  Admittedly even my best shot wasn't very interesting (seven stars and a black sky!) but it hinted that something is possible even with short exposures.

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Refractors are less problematic than reflectors for brining cameras to focus, you will need to try it to know for sure though. If you are able to focus an eyepiece with and without the diagonal you probably have enough focuser travel for the camera though.

The other posters are right in that f16 is too slow for DSO work, of course you could bring this down with a reducer/flattener but you would still have the problem of needing a stable mount.

Don't discount solar, the sun being rather bright is easy to image through a slow scope :D

Just make sure you have a full aperture solar filter and remove or cap your finder.

/Dan

Sent from my iPad using Tapatalk

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I've taken a chance on ordering the simplest t2 ring-nosepieces adaptor. We'll see if it works. I'll report back in due course.

Cheers

Dave

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I am afraid as I said, thinking like a photographer puts you at a disadvantage because you will have to 'unlearn' so much.

'Crop factor' has nothing at all to do with magnification or focal length. It is simply the field of view of your camera sensor. A 300mm lens on a M4/3 is still a 300mm focal length, you just see a smaller part of the scene than you would if you used a full frame sensor. What counts is the optical resolution. How many arcseconds per pixel does your focal length and sensor combination give you?

I found some details on your Sony so here are a couple of examples for you. You pixels are 4.78 microns in size. 1250mm focal length gives you 0.79 arcseconds per pixel. The moon is about 0.5° or about 2000 arcseconds in apparent diameter. That means it will cover 2,500 pixels, so a good image size. Actually it will look something like this and with good focus in the right night with plenty of contrast in craters along the terminator has the potential for a stunning shot :)

post-5915-0-01115300-1448207592_thumb.jp

Saturn is about 17 arcseconds in apparent diameter. That means it will cover only about 20 pixels and will look something like this

post-5915-0-72358700-1448207670_thumb.jp

Drop in a 2x TC and you get 40 pixels across

post-5915-0-39924200-1448207719_thumb.jp

Using your existing camera lenses for starfields and clusters like the Pleiades will give you better results than using your telescope. Putting a DSLR and lens on a simple tracking mount like the Vixen Polarie or SkyWatcher Star Adventurer will give great results and a lot of enjoyment.

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I am afraid as I said, thinking like a photographer puts you at a disadvantage because you will have to 'unlearn' so much.

'Crop factor' has nothing at all to do with magnification or focal length. It is simply the field of view of your camera sensor. A 300mm lens on a M4/3 is still a 300mm focal length, you just see a smaller part of the scene than you would if you used a full frame sensor. What counts is the optical resolution. How many arcseconds per pixel does your focal length and sensor combination give you?

I found some details on your Sony so here are a couple of examples for you. You pixels are 4.78 microns in size. 1250mm focal length gives you 0.79 arcseconds per pixel. The moon is about 0.5° or about 2000 arcseconds in apparent diameter. That means it will cover 2,500 pixels, so a good image size. Actually it will look something like this and with good focus in the right night with plenty of contrast in craters along the terminator has the potential for a stunning shot :)

attachicon.gifimage.jpg

Saturn is about 17 arcseconds in apparent diameter. That means it will cover only about 20 pixels and will look something like this

attachicon.gifimage.jpg

Drop in a 2x TC and you get 40 pixels across

attachicon.gifimage.jpg

Using your existing camera lenses for starfields and clusters like the Pleiades will give you better results than using your telescope. Putting a DSLR and lens on a simple tracking mount like the Vixen Polarie or SkyWatcher Star Adventurer will give great results and a lot of enjoyment.

Thank you for doing that, gets the point across very well!  :laugh:

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As Rik says if you already have a bunch of photography equipment the a Sky Watcher Star Adventurer is the best way into astrophotography, you may even have a suitable tripod and you could try mounting your scope on it, nothing ventured :grin: 

Dave 

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I've taken a chance on ordering the simplest t2 ring-nosepieces adaptor. We'll see if it works. I'll report back in due course.

Cheers

Dave

Hi Rik

Thanks again for all your help.

One point I'd like to make: of course you are correct in saying that the crop factor doesn't change the physical focal length. However, it does make a difference when comparing sensors of different sizes but the same pixel count: the pixel density is higher. For example, if I compare my m4/3 16MP to a full frame 16MP, my m4/3 camera is concentrating all its pixels in an area 1/4 of that of the full frame.  Which means I can blow up the frame 2x bigger compared to the full frame without loss of resolution (assuming the scope has sufficient resolution to support the magnification). The downside is smaller pixels, more noise and less dynamic range.

I had a quick go at the moon with my camera lens (300mm f4 + 2x teleconverter + m4/3 panny g6 = 1200mm equivalent compared to full frame with same lens).  I downloaded and installed some free stacking software (PIPP and Autostakkart). Don't really know what I'm doing with it but here's my first attempt:post-47707-0-29949700-1448276618_thumb.j

I shot about 60 frames and selected the best 15 (100% - 80% quality). The pic makes a decent 7x7 inch print as long as you don't try and look too closely ;-)

I'm not sure what is the biggest quality constraint: the mount, the lens, shutter speed, camera resolution, seeing, magnification, number of frames, processing but sharpness is a long way from great, even with loads of processing...

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Biggest quality restraint is what's called the "seeing" basically how wobbly the Moon looks, this can vary dramatically from second to second which is why folks use high frame rate video cameras.

Second restraint is achieving perfect focus hampered by the above mentioned seeing. :)

Dave

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Biggest quality restraint is what's called the "seeing" basically how wobbly the Moon looks, this can vary dramatically from second to second which is why folks use high frame rate video cameras.

Second restraint is achieving perfect focus hampered by the above mentioned seeing. :)

Dave

Focus with my camera didn't seem to be a problem even though it is easily disturbed. 10x mag in the viewfinder + focus peaking seems to do the trick. I used the electronic shutter to avoid vibrations from a clacking shutter and fast burst mode but no cable release. Should have used one. I might try HD video with the special 2x mode that panny use (this uses a 2MP slice of the sensor rather than digital zoom and supposedly avoids line skipping/downsizing problems).

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That's a cracking shot. You approached it just the right way, with the right software set as well :)

As Davey-T says, 'seeing' is the biggest pain and this is the reason for taking lots of shots and stacking. With the moon at over half full you will start to loose contrast in the craters. About first quarter usually gives the most dramatic shots.

Yes, I know what mean about comparing different size sensors with the same pixel count, but that isn't generally the way astrophotographers approach it. The reason for calculating optical resolution in arcseconds per pixel is to be able to match sensors to optics taking account of local 'seeing' conditions. For deep sky astrophotography, values of about 1-3"/pix are considered the 'sweet spot'. For lunar or planetary photography you can go much lower than this assuming you are shooting lots of frames and stacking (exactly as you did). These would typically be several thousand frames, keeping the best several hundred in the final stack. For that reason, giving your video mode could be well worth a try :)

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That's a cracking shot. You approached it just the right way, with the right software set as well :)

As Davey-T says, 'seeing' is the biggest pain and this is the reason for taking lots of shots and stacking. With the moon at over half full you will start to loose contrast in the craters. About first quarter usually gives the most dramatic shots.

Yes, I know what mean about comparing different size sensors with the same pixel count, but that isn't generally the way astrophotographers approach it. The reason for calculating optical resolution in arcseconds per pixel is to be able to match sensors to optics taking account of local 'seeing' conditions. For deep sky astrophotography, values of about 1-3"/pix are considered the 'sweet spot'. For lunar or planetary photography you can go much lower than this assuming you are shooting lots of frames and stacking (exactly as you did). These would typically be several thousand frames, keeping the best several hundred in the final stack. For that reason, giving your video mode could be well worth a try :)

I tried it out on a chimney pot today. The Panasonic Ext Tele mode is really interesting. Usually with large sensor video, the camera downsamples or lines skips to get from the native 16MP to 2MP needed for each HD frame. Panny offer this special mode whereby instead of line skipping or downsizing, they just use a 2MP slice out the middle of the sensor. Effectively compared to standard HD video, it is gives you a 2.5x teleconverter built in with no loss of light or image quality. Handy when you need more reach from your lenses! Astrostakkert seems to be able to use the .mp4 files without conversion.

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I've used the Canon 60D that has a 640X480 1 to 1 pixel crop video mode that excels on planets, haven't tried it on the Moon.

Dave

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