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DSLR - Widefield. Where to start

Droogie 2001

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Droogie 2001

Droogie 2001

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Apologies if this has been raised before but I could not find a thread that answered all of my questions.

I have a Canon 1100D (Modded) I have been using this with my telescope at prime focus with reasonably pleasing results.

What I would like to have a go at is taking widefield images of the Milky Way and other astro widefield images.

1. Firstly the lenses. I purchased my DSLR without a lens so of course this is my first consideration. I have seen two of which are of particular interest and have been regarded as a good cost effective match with Astrophotgraphy. They go by several manufacturing names, Rokinon in the US and are also known as Samyang in the EU. The models are:

Rokinon 35mm F1.4 AS UMC Lens Canon EOS Fit

http://www.bristolcameras.co.uk/p-samyang-35mm-f1-4-as-umc-lens-canon-eos-fit.htm

Rokinon 16mm F2.0 Lens.

Both are manual focus.

From what I understand with the fast ratios you can get away with generally around 30 sec exposures. Will the Canon 1100d be a good match? I appreciate there maybe some vignetting and I also believe that my Astonomix CLS clip filter can be left within the main body.

This leads onto my 2nd question, mounting.

2. I have a Celestron AVX mount and it makes sense to use this when imaging with the camera. First is attaching it. Ideally I would like to use a dovetail and attached this to the DSLR. I have heard that a ball joint can help with imaging but I guess the mount can be moved as an alternative. Does anyone have any links to suitable mountings?

Also do I need to Polar Align if I want to take exposures longer than say 30secs? What would be the limit when polar aligned be 60 secs -10 mins?.

On the subject of Polar Aligning how do I go about this? Do I Polar Align as normal with my Telescope and then swapped the two over!?

3. Focusing & Software.I use BYEOS so I am guessing I could use this as normal? As for focusing do I use Live view and manually focus the lens? I usually use a Bahtinov mask with my OTA but this clearly would not be possible here.

4. Any other considerations?

Any suggestions or help would be much appreciated. Thanks.

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Alien 13

Alien 13

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The two lenses you mention are good performers but I would add the new 50mm F1.8 STM to the list.

With the wide angle of these lenses it would probably be better to use a ball head mounted on a dovetail or you might end up imaging part of your mount it also allows you to frame the image.

Focussing just needs liveview at x10 either on camera or through BYEOS.

A general polar alignment is normally good enough for about 1-2 mins at these wide angles and should capture lots of detail.

Alan

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jambouk

jambouk

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50mm is ok if you are on a tracking mount, but gives a relatively narrow field of view otherwise in myopinion, though i've done plenty of atar trails with my nifty fifty.

I recently got the samyang 24mm, but wish i'd gone for aomwthing even wider.

Dew is a big problem and now i have a dedicated dslr dew controller and dew band which solves the issue.

There are lots of online resources on the topic, and one book by robert reeves is [was] available online as a pdf. Many books at not up to speed/date woth modern dslr cameras, but the principles and ideas are still very applicable.

James

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Droogie 2001

Droogie 2001

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Thanks for the responses. So for tracking I would be using my AVX mount. Therefore do I align with my wide field WO Star 71 OTA and then simply switch the devices over?

Jambouk. You say that you should have gone wider do you mean you would like a 35mm or even 50mm?

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Davey-T

Davey-T

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I've seen a setup somewhere of the DSLR mounted on a ball head on the counter weight bar so you could leave the scope in place.

You can input various lenses into Stellarium to see the FOV you will get.

Dave

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jambouk

jambouk

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When i said wider, i meant, as happt-kat suggested, i wish i had gone for a shorter focal length lens (<24mm) so that the field of view was even greater.

This is a star trail from my light polluted back garden taken at 24mm on my canon 6d on a static tripod:

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davedownsouth

davedownsouth

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I have just bought one of these from FLO for attaching my camera directly to a dovetail placed on the top of my scopes tube ring.  It has not arrive yet (only ordered it yesterday), but hopefully this will mean I will soon be able to get wide field shots of what I am imaging with the scope using just one mount :).

http://www.firstlightoptics.com/adm-camera-mounting-adapters/adm-camera-mount-with-clamp.html

NB.  50 mm is my fav. lens.  Can just about get Orion in it  :cool:

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jambouk

jambouk

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As for mounting the camera on the mount, yes you can put it on a telescope, but i find that is unnecessary, and for tracked imaged i just use the dslr quick shoe which my static tripod came with and attach the shoe to the bottom of the camera (or to the camera battery grip more commonly if away from home (if at home often use mains power for the dslr so don't need the battery grip)) and then clamp the camera in place in the saddle of the mount that way.

If you don't have a shoe, get one like this:

http://www.amazon.co.uk/gp/aw/d/B000YCYT1A/ref=mp_s_a_1_4?qid=1438466637&sr=8-4π=AC_SX110_SY165&keywords=Dslr+quick+shoe&dpPl=1&dpID=319IB7ptiSL&ref=plSrch

To star align with just the dslr, just use the dslr like a scope; start at the home position, slew to the first star and use live view to centre the star in the centre of the fov using rhe handset, then if you want it as accurate as possible zoom in on live view on a box in the middle lf the screen and keep centring the star each time you zoom in a bit more. Then accept and slew to the next star and repeat.

James

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Knight of Clear Skies

Knight of Clear Skies

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Hope you enjoy getting into widefield imaging. There's a collection of images I've taken with various lenses from 18mm to 200mm FL (with the odd telescope shot thrown in) in this Flickr album if you are interested, it includes info on the lenses, exposure times and f-stops used.

To answer a few of your specific questions:

1. Your 1100D is entirely suitable for lens imaging, I use one myself. Longer exposures will improves the signal-to-noise ratio but the longest exposure time you can use may be limited by your local sky brightness/focal ratio and accuracy of your tracking.

The lenses you have highlighted would probably be good but are likely require stopping down to prevent coma at the edges, so you may not benefit from their very fast focal ratios. It's probably worth searching online to see what aperture values people are using with them. I like to use cheap 2nd-hand prime m42 lenses, although I'm very tempted by the Canon 200mm f2.8 L.

2. Polar alignment is very forgiving at short focal lengths, I managed to consistently take 2 minute subs at 50mm before I bought a polar scope. With longer lenses alignment is more critical, I can get unguided 2 minute subs at 135mm with my mount but polar alignment probably isn't the limiting factor.

3. You can get Bahtinov masks that are small enough to fit camera lenses but I just focus using live-view. Focussing on a star a third of the way from the edge will give a better focus across the whole frame.

Hope that's of some help.

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kalasinman

kalasinman

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What you deem widefield determines what you will settle on. To some , widefield is 3+ degrees FOV, to others 45 degrees.

I have a number of lenses going from 12mm to 200mm for widefield. Current crazy idea for 3x4 degree FOV is a 6x7 lens adapted to APC sensor.  No stopping down required because of huge crop already by small sensor . Although the lens is a 200mm, the net is closer to an APC lens at 300mm. So, if the skies ever clear, I should have a 300mm with a usable fast f/4. BTW the aperture is around 75mm.

Wish me luck. :rolleyes:

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chrisvdberge

chrisvdberge

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With very wide field I would just focus during the day and fix the focus with a piece of tape. Much easier!

As for lenses; the Rokinon's (or Samyangs) are excellent indeed. Even cheaper is the (already mentioned) 50mm. I'm a Nikon user so I'm not sure, but I think Canon also has a cheap (100 euro's) 1.8 version that is great

For alignment (and targeting) you can always put a red dot finder on the hot shoe of your dslr. 

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Droogie 2001

Droogie 2001

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I have gone with buying a Rokinon (Samyang) 16mm F2.8

Already have a tripod and the lens should arrive early part of the week. Typically cloud looks like it is going to delay first light. Especially annoying as Perseids are due to be good Tue-Thurs and these would make a nice test target.

Anyway really looking forward to seeing what results I can get.

Thanks for everyone's advice and suggestions.

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kalasinman

kalasinman

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With very wide field I would just focus during the day and fix the focus with a piece of tape. Much easier!

As for lenses; the Rokinon's (or Samyangs) are excellent indeed. Even cheaper is the (already mentioned) 50mm. I'm a Nikon user so I'm not sure, but I think Canon also has a cheap (100 euro's) 1.8 version that is great

For alignment (and targeting) you can always put a red dot finder on the hot shoe of your dslr. 

I've been wanting to do that for some , even just a green laser, but I haven't found any adapters to make it work.

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