Comparison: 2" vs 1.25" Prime Focus DSLR Adapters
Posted: 29 August 2014
2" to T-Thread Adapter
Third Planet Optics (TPO)
Oceanside Photo & Telescope
As I've switched to mostly 2" eyepieces and filters, it made sense to switch from a 1.25" prime focus adapter for my D7000 DSLR to a 2" adapter for prime focus astrophotography. My 1.25" adapter is from the OPT Camera Adapter (click the link for my review). I purchased a TPO 2" to T-Thread Adapter from Oceanside Photo & Telescope (OPT).
There are no end caps supplied with the 2" adapter, but it does come in a plastic bag. The adapter is threaded to accept 2" filters. The adapter is made of lightweight metal and seems to be adequate for the job. It fit fine in my 2" holders.
To attach the 2" adapter to the DSLR a T-Ring is needed (same ring as I use with my 1.25" adapter), as seen here:
This photo of the 1.25" adapter beside the 2" adapter clearly shows how much more light can reach the camera through the 2" adapter:
With both adapters there is some vignetting seen at the top of the camera viewfinder. However, no vignetting is evident in the following full-frame (unedited) moon photos.
Of course, lunar photography doesn't tell the whole story. On 23 and 27 August 2014, I did some comparison prime focus photos of Comet C/2014 E2 Jacques, which just happened to be the constellation of Cassiopeia. The Antares f/6.3 focal reducer was used and the D7000 DSLR was mounted using the Meade 2" star diagonal. Some vignetting is visible in the upper left and right corners with the 1.25" adapter but none is visible with the 2" adapter in these unedited, 3 minutes, ISO 6400, images.
(Some digital noise is visible along the frames edges in both images.)
I also tested using a 2" visual back (no diagonal) at prime focus + focal reducer (unedited, 3 minutes, ISO 6400):
Vignetting at all four corners is more obvious with the 1.25" adapter, although there is some with the 2" adapter. The vignetting is more extensive when using the visual back than when using the star diagonal.
I like the TPO 2" prime focus adapter. It is well made and certainly avoids most of the vignetting seen in prime focus images using my Nikon D7000 DSLR. In situations where I don't need to guide (typically required for exposures longer than 3-5 minutes), using the 2" adapter will be my main adapter.
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