nifty-fifty widefield imaging

[nicks90]

good morning everyone!

My continuing efforts at widefield imaging are starting to come along further now - with the acquisition of a 50mm prime lens (well actually 2) for my samsung nx100.

but I do have a couple of questions....

at the moment i'm doing my widefield with the standard samsung kit lens, which at 50mm is f5. It is sharp across the FoV when taking normal daytime pictures and the widefields i;ve done have shown no abherations or shadows etc on stars up to the edge. So its a good lens, just way too slow.

So i;ve managed to bag two classic 50mm primes - a Canon FD 50mm f1.4 and a pentax 50mm F1.8

the reviews for both these are very good - however they do say the canon is 'soft' at f1.4, whereas the pentax is sharp even wide open. Is this really important when doing widefield AP, or will stacking lots of short subs negate the issue of softness. Is it something I would even notice?

So I'm just wondering if its even worth shooting at f1.4, or stopping it down to F2 and doing a comparison of both lenses at almost identical F ratios and see which is best and flogging the other. Will F1.4 make a really big noticeable difference over F1.8?

any help on this would be appreciated.

Nick

[Leveye]

Don't worry about that using a camera lens for wide field. Concentrate on focus. I have many vintage 50mm lenses and they all shine wide open using them for astrophotography. I personally don't like the star patterns when stopping down anyways. Check into the Ashai/Takumar and Nikkor lenses for the real amazing results for a lenses under 100 dollars. Look up!

[niccodeamus]

I may begin with the standard "I haven't tried this, but..."

I sort of have tried it but I currently have no tracking or guiding mechanism.  If you are tracking, the aperture is less of an issue and go for sharpness, stopping it down a bit. I have a Canon EF 1.4 and a 8 second exposure is over exposed due to LP, if can get in the dark, sellotape the camera to your Dob, keep the ISO down, you should be good at f3.2, or less, for a minute or so.  and if you stack a few....

[Alien 13]

There are a few good old lenses that work fine wide open my 135mm is pin sharp across the whole FOV but what it and and most lenses suffer from is star bloat on long exposures, star bloat can be processed out but misshaped stars cant so take a few shots at 4 second exposures and check the star shapes in the corners.

I also find that my kit lens which is an EF-S 18-55mm IS11 is also pin sharp in the corners at 18mm and 50mm FL.

PS that canon F1.4  you have would make a great video lens.

Alan

[nicks90]

i will be tracking - i've just installed a camera thread on to the top of the dob and will therefore be able to do 30sec exposures or so without worrying about field rotation too much and using DSS to stack / crop image to remove any rotation.

However one step forward - two steps back... the dob isnt tracking properly at the moment, so I need to investigate the clutches.

at the moment, I;m using a tripod and doing 5-10sec exposures when pointing southwards and stacking them, mostly at 50mm F5 with the kit lens. When pointing north, I can extend that to 20 seconds without trailing. But the idea of having a MUCH faster lens should mean I get more detail for the same exposures. Upping that to 30 seconds with my dob will hopefully mean loads of data for stacking! So although having a super fast prime lens isnt the be-all-and-end-all, I am still limited on the data I will receive and i'm hoping going from an F5 to F1.7 will make a big difference.

hope......

[mitchelln]

sellotape the camera to your Dob, keep the ISO down, you should be good at f3.2, or less, for a minute or so.  and if you stack a few....

Now why didn't I think of that? Does anyone know if there is such a thing as a finder bracket to camera tripod mount screw adapter so the camera can be attached by the SW finder shoe?

[Johnny666666]

Now why didn't I think of that? Does anyone know if there is such a thing as a finder bracket to camera tripod mount screw adapter so the camera can be attached by the SW finder shoe?

I think it's a 'dove tail' or mounting bar you need. I actually got a spare with my SW150P and it has the correct 1/4" BSW threaded holes for camera mounting - I use part of an old flash bracket (google it to see what I mean) that simply screws into the holes on the dove tail and the camera screws onto that. I can simply take the scope off the mount and put the mounting bar (with my camera on that) on to the mount

[hobsey]

Now why didn't I think of that? Does anyone know if there is such a thing as a finder bracket to camera tripod mount screw adapter so the camera can be attached by the SW finder shoe?

Why not buy a tube ring as most of the time they have a camera mount already on them allowing you to just screw your camera on to it.

[mitchelln]

I think it's a 'dove tail' or mounting bar you need. I actually got a spare with my SW150P and it has the correct 1/4" BSW threaded holes for camera mounting - I use part of an old flash bracket (google it to see what I mean) that simply screws into the holes on the dove tail and the camera screws onto that. I can simply take the scope off the mount and put the mounting bar (with my camera on that) on to the mount

Thanks for that. I'll investigate!

Why not buy a tube ring as most of the time they have a camera mount already on them allowing you to just screw your camera on to it.

Thanks for the suggestion, but a tube ring is impractical for my 12" Dobo

[hobsey]

Thanks for the suggestion, but a tube ring is impractical for my 12" Dobo

My bad, should have checked what scope you had first. Seeing its a flextube might prove difficult also.

[Knight of Clear Skies]

As a point of reference, here's a recent effort of mine using a Canon 50mm lens at f1.8:

(15 second exposures at ISO 1600, 5 minutes data in total.)

I found star bloat became more apparent when stretching the histogram to bring out the Pinwheel Galaxy at centre top. I'm not sure if better processing (maybe a star mask?) or stepping down is the solution.

Here's a close crop of M67 taken with the same lens at f2.8 (20 sec subs, 6 minutes total):

Hope that is some help, I'm just starting out with my 50mm lens and am not sure how to get the best out of it. A side-by-side comparison at different aperture settings would be a good idea, on both bright and dim targets.

[nicks90]

Those are brilliant pictures!

I'm getting giddy with excitement to have a go now, so apologies if its cloudy until the full moon is up - my fault!

[Psychobilly]

Here's one of mine...

Sky at Night CD Sept 2010 Cygnus Nebs by psmithuk, on Flickr

and another...

[niccodeamus]

i was being slightly facetious when I said use sellotape.  I actually use large rubber bands and a bit of wood under the lens to keep everything in line.  works quite well, of course dependant on the Frustration Mount working as well as it can.  I am looking forward to learning more about the wide field image and its techniques.  i am sort of hoping it isn't so complicated as the DSO stuff 

Here's one of mine...

Sky at Night CD Sept 2010 Cygnus Nebs by psmithuk, on Flickr

and another...

these are brilliant.  are they tracked and stacked? is the purple a cast/gradient artefact of some sort?

[Psychobilly]

Yes tracked and stacked using an EQ3-Pro the Sag-Oph one was from a cliff top on the ally tripod...

Sent from my GT-I9505 using Tapatalk

[Knight of Clear Skies]

Those are brilliant images Peter, if I can get half way to that standard I'll be very happy indeed.

[Beulah]

I'm now a member of the Nifty Fifty Club, managed to snag a Mark 1 today...really inspired by what has been shown on this thread...

[laser_jock99]

50mm lenses are great fun for astro work. My Nikon F1.4 has a 49mm filter thread, with a step down ring I can screw on 48mm narrowband astro filters to image the faint nebulas- some of which are very large in the sky.

This experimental Cygnus widefield image was achieved by using a 7nm Ha filter for 10 minutes at F1.4, covering the lens, stopping down F2.8,  unscrewing the filter and exposing 3 minutes more- all in one shot.

No Photoshop jiggery pokery- just a steady hand!