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Back Focus distance for DSLR lenses?

SteveL

By SteveL
in Discussions - Cameras

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MartinB

MartinB

Posted
Posted

Sorry Steve, could you clarify for me, I'm pretty slow on the uptake with this, which filter drawer do you have and how did you sort out the bit at the bottom for attaching to the mount/dovetail?

I have a Gerd Neuman drawer. It's very nice although it's round shape doesn't lend itself to attaching to a mount, and the QHY 8 doesn't have any means of attaching either, hence my problem

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Psychobilly

Psychobilly

Posted
Posted

Look forward to seeing the results :(

Here's a ltille "experiment" I did when I started playing about with DSLR lenses On the MEade DSI... I used to piggy back The DSI and SLR lenses on the ETX105..

http://picasaweb.google.co.uk/PsychoBillyUK/CCDImagersWithSLRLenses#5162853307507138018

As I was desperate to have something to Image Comet Holmes with...

http://picasaweb.google.co.uk/PsychoBillyUK/CCDImagersWithSLRLenses#5162855983271763730

http://picasaweb.google.co.uk/PsychoBillyUK/AstroPhotography#5162679610439750018

Thats what really kicked off the intrest in Astrophotography.......

Billy...

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Erwin Kats

Erwin Kats

Posted
Posted

look out with older lenses, in normal photography you mostly get CA ( chromatic aberration )

in digital photography you get purple halo's around stars, if you go HA or mono, with the qhy8 i do not know what will hapen.

like billy sayed earlier, Prime lenses work greater, but i never used them on a CCD, only with DSLR.

canon ef L 200 F2,8 the 50mm F1,8 isn't expensive btw ( around 120 euro's new )

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Merlin66

Merlin66

Posted
Posted

A minus UV (skylight A1 type) will improve colour images from older lenses. For narrow band imaging ie Ha/O iii it won't affect the image if focus is OK.

Just remember that they were designed for film resolution (approx 20micron) not for 8 micron CCD sensors. Mind you they still can do a good/ great job for the money!

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Erwin Kats

Erwin Kats

Posted
Posted
A minus UV (skylight A1 type) will improve colour images from older lenses. For narrow band imaging ie Ha/O iii it won't affect the image if focus is OK.

Just remember that they were designed for film resolution (approx 20micron) not for 8 micron CCD sensors. Mind you they still can do a good/ great job for the money!

indeed, because he got that filter system to apply filter.

most astro filters can not be applyed on the aperture of most lenses ( 77mm etc )

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astro_dt

astro_dt

Posted
Posted

Hi Steve

I have used a Meade DSI and camera lens to get images. I bought old lens from ebay and coupled them via M42 threads. As the automatic focus and aperture isn't required I bought broken lens that were stuck wide open for next to nothing.

Loads of good advice in previous posts but two things I would point you to.

1. Get a set of M42 extension rings, these help achieve the back focus and may help you with filters etc. I use these on all sorts of set up now.

2. You will want to add a finder. I used an exhaust clamp bracket that fits round one of the extension tubes. (don't have an image with me at the moment but there are pictures on my website in the projects section).

Have fun

Danny

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steppenwolf

steppenwolf

Posted
Posted
I hear of people having to step down one click when using them for astro work. Is that a good rule of thumb, or only for faster lenses that go down to f/1.8-2.8?
This can be a little bit of a variable feast but one stop is always a good compromise as it tends to improve the image a little without throwing away all that wide aperture. The downside is that the leaves of the iris impart multiple diffraction spikes on bright stars, an effect that you may or may not like!

I only use OSC cameras so only ever really need a single filter, either IDAS LP or Ha so I designed my own adapter which has internal threads for a filter and this works very well indeed with all my Canon lenses. I can also now add a Canon teleconverter for extra flexibility. Here it is with my Canon 200L telephoto and then on its own:-

canon_adapter_5.jpg

canon_adapter_4.jpg

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SteveL

SteveL

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Well, I am now sorted. A huge thank you goes to Gerd Neumann for his help with this.

I ordered one of the filter drawers, plus the Nikon adapter, and stuck the M25C on the end. It needed a 2mm spacer to get it to focus correctly, which he sent immediately (while I improvised with my own custom cardboard spacers :) ).

nikon_m25c_001.jpg

The filter drawer itself is held in place by two sprung loaded inserts just inside the edge of the hole where the drawer goes in. You can adjust the pressure of these two inserts using the grub screws on the outside of the body. They can supply more than enough grip to hold the filter drawer in place, even when everything is hanging upside down at crazy angles.

nikon_m25c_002.jpg

Along with the spacer, I also ordered an Astronomik T2 UV/IR filter, so I could replace the nosepiece on my QHY8 with something just a little shorter, and enable this camera to be used with the Nikon lenses. As it happens, using the Astronomik T2 filter and the filter drawer is EXACTLY the correct back focus distance :)

nikon_qhy8_001.jpg

nikon_qhy8_002.jpg

There is an option when buying the filter drawer to request that one side of the main body has a 1/2" UNC thread added so that you can mount the entire setup on a normal camera tripod head. This is useful if the camera body doesnt have its own tripod mounting hole.

nikon_qhy8_003.jpg

I have had some test shots with the M25C a while back, but using the Ha filter made focusing on tiny tiny stars really difficult. I`ll post some RGB images soon.

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Psychobilly

Psychobilly

Posted
Posted

Yeah canon and their stupidly short mount to FP distance :) Nikon havent changed theirs from their very first 35 SLR days and ther should be a lot of quality glass out there Look for Nikkor rather than Nikon... Nikkor is the premium "optics" sub-brand of Nikkon...

Peter....

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Psychobilly

Psychobilly

Posted
Posted

I use sigma llenses with my nikon kit... 50mm macro 180mm apo macro and 10-20mm they are ok... I have a pair of Nikkor AF-S zooms as well they are different animals designed to work with full frame sensors as well...

There are some nice fast sigma primes as well ...

and then there's this...

187_small.jpg

Sigma - Lenses

There are also some nice sensible ones...

Trawl the Bay of E .... and see what comes up...

Peter...

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