ASTRO: UltraWide Adapter for DSLRs

For those who use DSLRs. The UltraWide adapter seems to have no
advantage over the standard T-mount when it comes to APS-C size
sensors like my Canon 40D. The attached flat field images were taken
with a NP-127 at F/5.2.

Robert Price wrote:
For those who use DSLRs. The UltraWide adapter seems to have no
advantage over the standard T-mount when it comes to APS-C size
sensors like my Canon 40D. The attached flat field images were taken
with a NP-127 at F/5.2.

I don't understand what the adapter is for. Is it a compressor?

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

Rick

The top left image is the UltraWide adapter attached to my Canon 40D.
The top right image is a Williams Optics T-adapter and T-ring attached
to my Canon 40D. The corresponding bottom images are flat fields with
greately exaggerated levels to show the field difference in intensity.
The adapter attaches the camera to a 2 inch eyepiece holder. The
T-adapter has a 1.5 inch opening, the UltraWide adapter a 1.85 inch
opening limited by the tube inside diameter.
Robert

On Sat, 04 Apr 2009 20:28:30 -0500, Rick Johnson
wrote:



Robert Price wrote:
For those who use DSLRs. The UltraWide adapter seems to have no
advantage over the standard T-mount when it comes to APS-C size
sensors like my Canon 40D. The attached flat field images were taken
with a NP-127 at F/5.2.

I don't understand what the adapter is for. Is it a compressor?

Rick

OK I follow now. For some reason I had them reversed, probably because
I saw "adapter" on the right one and figured that was part of the
"ultrawide adapter" name. The T adapter I used with my 35mm camera had
an opening that matched that of the camera so didn't vignette any. Nor
does the T thread adapter for my STL-11000 block any of the 35mm film
size chip. The 1.75" baffle tube in the LX200R about 6" in front of the
camera does vignette some however but that flat fields out easily. I
guess I didn't realize some really reduced the opening. Must have
something to do with the way the lens attaches to the body. At least
you found a solution.

Rick

Robert Price wrote:

Rick

The top left image is the UltraWide adapter attached to my Canon 40D.
The top right image is a Williams Optics T-adapter and T-ring attached
to my Canon 40D. The corresponding bottom images are flat fields with
greately exaggerated levels to show the field difference in intensity.
The adapter attaches the camera to a 2 inch eyepiece holder. The
T-adapter has a 1.5 inch opening, the UltraWide adapter a 1.85 inch
opening limited by the tube inside diameter.
Robert

On Sat, 04 Apr 2009 20:28:30 -0500, Rick Johnson
wrote:



Robert Price wrote:

For those who use DSLRs. The UltraWide adapter seems to have no
advantage over the standard T-mount when it comes to APS-C size
sensors like my Canon 40D. The attached flat field images were taken
with a NP-127 at F/5.2.

I don't understand what the adapter is for. Is it a compressor?

Rick



--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

On Sun, 05 Apr 2009 12:39:53 -0500, Rick Johnson
wrote:

OK I follow now. For some reason I had them reversed, probably because
I saw "adapter" on the right one and figured that was part of the
"ultrawide adapter" name. The T adapter I used with my 35mm camera had
an opening that matched that of the camera so didn't vignette any. Nor
does the T thread adapter for my STL-11000 block any of the 35mm film
size chip. The 1.75" baffle tube in the LX200R about 6" in front of the
camera does vignette some however but that flat fields out easily. I
guess I didn't realize some really reduced the opening. Must have
something to do with the way the lens attaches to the body. At least
you found a solution.

All t-mount to camera adapters are standardized with a 42 mm diameter
by 0.75 mm pitch female thread. The telescope to t-mount adapter has
a male 42 mm diameter by 0.75 mm thread. For strength the wall of the
telescope to t-mount adapter has to be at least a couple of mm thick,
making the maximum inside diameter no more than 38 mm. When the rear
lens element of the lens is distant from the t-mount to camera
adapter, as it is with telescopes, you will be fully illuminated
inside a circle that is necessarily smaller than 38 mm. The amount of
light falloff depends on the exact geometry. The EOS wide adapter
doesn't have a t-thread inside, allowing it to use as much of the 54
mm diameter of the EOS mount it needs. With a 2" outside diameter
barrel and a wall thickness of about 2 mm, the EOS wide adapter can
have an inside diameter up to 47 mm. This should let you have a fully
illuminated field larger than with a t-mount to EOS adapter. To get
the most benefit from the large inside diameter, the barrel of the EOS
wide adapter should be as short as possible.

Bud