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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. |
#2
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ASTRO: UltraWide Adapter for DSLRs
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". |
#3
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ASTRO: UltraWide Adapter for DSLRs
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 |
#4
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ASTRO: UltraWide Adapter for DSLRs
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". |
#5
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ASTRO: UltraWide Adapter for DSLRs
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 |
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