CCD IMAGERS WITH SLR LENSES Last updated: 11 September 2007

Subject:	CCD Imagers with SLR Lenses
Sent:	Thursday, September 6, 2007 09:22:23
From:	PETER SMITH (psmithuk@btinternet.com)
I have been reading through your site archives and came across
discussions about using the CCD DSI,LPI and Toucam II Pro "imagers" with
SLR Lenses - I am not claiming any originality as I have seen these
ideas elsewhere on your site and on other Internet sites..

Seeing as I have quite a collection of SLR lenses I decided to look at
making adaptors for them to take 1.25" eyepieces and imagers. A quick
search of the Internet found the following information about the lens
mount to focal plane distances for various SLR mounts
 
Lens             Mount - FP
Minolta AF  43.5
M42            45.6
Nikon AF    46.5
Canon EOS 44
 
A careful session with the Vernier gave me these measurements for the
various "imagers" in my collection...
 
Imager           Nose Piece to CCD
Toucam Pro   42
Meade LPI    25
Meade DSI    30 + 1.5 (Filter)
 
All dims in mm CCD distances to front of filter on CCD

It looks like my quest to make an adaptor that will work with all three
images will be im possible or at least complex due to the different
distances to the CCD chip in each...Anyway nothing like a quick lash up
to try out an idea (only problem is do you ever bother to make the
finished article if the lash up works..)



The Minolta Adaptor is made from a rear lens cap which has had a
"custom"  1.25" barrel fitted

The M42 uses an extension ring and "custom" 1.25" barrel fitted the
difference in the OD and ID is so small tha a nut has been fixed to the
barrel to allow the locking screw to be fitted.

The bottom adaptor allows me to mount a camera into the eyepiece port of
the ETX for wide-field DSLR Shots etc

I have found the good old manual focus M42 lenses to be the best as the
focus mechanism is nicely "damped" whereas the AF lenses are bery loose
and prone to "drifting"

The following images are samples from a Meade DSI Color and Meade LPI
connected to a 300mm F5 M42 lens
 




 
I have yet to try any "astro" shots using the DSI on the SLR lenses - I
use a Seben 8-24X zoom made parafocal with the DSI to set rough focus.
 
Regards,
Peter SMith (UK)

Subject:	DSI - SLR Adaptors First Light 
Sent:	Monday, September 10, 2007 14:27:17
From:	PETER SMITH (psmithuk@btinternet.com)
Hot off the Laptop these are the "First light" stellar images taken with
the DSI Color attached to SLR lenses from my very light polluted and
restricted view back yard...

The lenses used are a 300mm F5 and 135mm F3.5 the images are taken with
the DSI mounted on a standard camera tripod so the only "tracking" was
via the autostar envisage software the 300mm image is in the vicinity of
Polaris and the 135mm image is in the vicintiy of Vega. I stacked  short
(2-4s) exposures with dark subtraction. The photo tripod and very
crudely mounted (good old duct tape) DSI/Lens combo is why I say in the
vivinity of....

Encouraging first night out now all I need to do is make some space on
my crowed "105" to piggyback mount the DSI and SLR lenses.

Best Regards
 
Peter Smith UK

And more:

I decided that it might be a good idea to try and obtain an approximate
measurement of the effective FOV of the SLR lenses on the DSI Color so
that an appropriate lens selection for imaging astronomical objects can
be made.

I decided that the easiest ( for a quick and dirty "look see") way would
be to image a 1m steel rule at a known distance from the DSI/Lens combo
and then do the maths...(never liked maths it was a neccessary evil and
may be a bit rusty so take the results with a large pinch of  salt )

The attached image hopefully explains it all - well at least my thinking
and method.

The much smaller size of the ccd compared to the "35mm" frame results in
the apparent FOV being much smaller on the DSI which is the same as the
effective focal length being a lot longer ( same as you get when using
lenses on APS-C sized sensor DSLR's) it's just with the DSI the
multiplier is even greater...

It looks like the 300mm on the DSI color has a very similar FOV to the
26mm eyepiece on the ETX 105 which could be quite handy...Especially if
I can piggy back the DSI/Lens combo and still have the eyepiece port
available...hmmmmmm....

Still got to work out how to mount it all on a tracking mount.....Maybe
that's next :)
  
Best Regards,
 
Peter Smith (UK)

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