Review - Sensei Filter Step-Down Rings
Posted: 16 October 2020
Filter Step-Down Rings
While I was testing my newly received Explore Scientific 2" UHC Filter I began to wonder if I could use it with some of my DSLR lenses for wide-field sky astrophotography. First I needed to confirm that 2" astronomical filters had a standard thread pitch that could be used with camera lenses. 2" astronomical filters are 48mm diameter with 0.75mm pitch. At least, that's the theory as some astronomical filters may have 0.60mm pitch.
Next, I needed to find a step-down ring that would go from the 67mm filter size of my Nikon 70-300mm lens to the 48mm filter size. There was no single ring that would do that. However, B&H had a Sensei 52-48mm Step-Down Ring ($6) and a Sensei 67-52mm Step-Down Ring ($8) that should do what I needed. Since these were inexpensive I decided to give them a try and ordered them as part of a larger order (to avoid shipping charges for these small items).
The larger ring (Pro model) came in a plastic case; the smaller ring was just in a plastic bag. For purposes that was OK as the smaller ring will stay inserted into the larger ring. The 67-52mm Ring is aluminum with a matte black annodized finish and knurled side for easy attaching and removing. The 52-48mm lens is a black anodized metal without a knurled side. My Optolong 2" HA and OIII filters fit perfectly into the small ring as did my Explore Scientific 2" UHC filter.
Here are both rings on my Nikon 70-300mm FX lens (67mm filter thread) and the UHC filter on the lens.
I wondered if any vignetting (corner darkening) would occur with a 2" filter in place. As seen in these photos, there was no vignetting at 70mm (left) or 300mm (right). (Color due to the UHC filter and sunlight hitting the filter.)
However, using my Nikon 18-140mm DX lens there was some vignetting at shorter focal lengths (18mm left, 140mm right).
I mounted my D7200 DSLR with 70-300mm lens piggyback on my 12" LX600 telescope for some tests using 2" filters. The first images are without the rings or filters attached.
Heart & Soul Nebula, FL 135mm
Pleiades, FL 300mm, cropped
I then used some of my 2" filters to image the same objects.
Heart & Soul Nebula, FL 135mm, UHC & HA filters, unedited
Heart & Soul Nebula, FL 135mm, UHC & HA filters, cropped
Pleiades, FL 300mm, UHC filter, unedited
Pleiades, FL 300mm, UHC filter, cropped
While these initial images are not the greatest (and slightly out-of-focus) they do show that using 2" astronomical filters can sometimes bring out more details of an object.
The Sensei Filter Step-Down Rings do work with camera lens to allow the use of 2" astronomical filters when doing sky astrophotography. Their low cost will provide an effective accessory in your astrophotography kit. As with all astrophotography, as experience with using astronomical filters on your lenses grows, the results will be worth the small expense. I plan to continue using the Step-Down Rings with my camera lens for imaging more objects in my night sky and expect to get better results over time.
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