Description
QHY offers a very comprehensive and flexible adapter system that allows our cameras to achieve focus with a variety of accessories, including camera lens adapters, off-axis guiders, filter wheels and numerous optical systems. Based on users’ feedback, we provide fixed combination of adapter kits to meet mainstream needs of most users (e.g., Multi-Purpose Coma Corrector, Canon lens adapter, Nikon lens adapter, etc.). Users can choose the corresponding adapter set according to their needs to ensure focus. There is no need to measure and calculate the back focal length, choose adapters, and customize screws.
Back Focal Length Defined
Back Focal Length (BFL), in the commercial camera field, refers to the design distance from the center of the rear lens element to the surface of the sensor. Generally, the lens will only focus correctly at infinity if the camera’s back focal length meets the standard requirements provided by the lens manufacturer. This is also true for many Multi-Purpose Coma Correctors designed to be used on telescopes before the camera.
| Optical system | Back focal length required |
| Typical Multi-Purpose Coma Corrector | 55mm – 57.5mm |
| Canon 35mm lens | 44.1mm |
| Nikon 35mm lens | 46.5mm |
Note: Not all astrophotography gears have specific BFL requests, for example, some refractor scopes with internal flat correctors. In such cases, you needn’t use the following adapter kits. Instead, you can use a T ring or any adapter that can help connect your camera and scope.
"Back Focus Consumed" Defined
When an optical system requires the sensor of the camera to be located at a specific distance from the last optical element, mechanical spacer adapters are used to position the camera at the right location. If the camera system also includes a filter wheel and an OAG, for example, between the camera and the telescope, the space required for these items must be taken into account. As a simplified explanation, for example, if a telescope’s field flattener requires the camera focal plane to be 55mm behind the last optical element, and the filter wheel is 20mm thick, and the OAG is 10mm thick and the sensor is set 10mm inside the camera then these items all take up 20+10+10=40mm of the back focal distance. Still, the camera needs to be 55mm away so we need to add spacers that take up this remaining 15mm. This also means that if you have an optical system that requires 55mm of backfocus distance and your filter wheel is 25mm thick and the OAG is 20mm thick and the sensor in the camera is 17mm from the front plate, then these items take up 25+20+17=62mm of backfocus. Too much! In this case something has to go to reduce the total back focus distance of the camera to 55mm or a different optical configuration must be found.
For the convenience of calculation, all the data displayed are the increase in the back focal length taken up by using the adapter, which is not necessarily equal to the thickness of the component itself. All the adapter data provided by QHYCCD are based on the focal length increment.
Recommend Combinations
At present, our adapter combinations for monochrome cameras are based on the focal length of the following combinations, which are also our recommended combinations. If you use combinations other than those recommended, the adapter set may not achieve its purpose.
Please refer to: https://www.qhyccd.com/product/astrophotography-combos/
Adapter Kits Introduction
Note: in 55mm solutions, if you do not want to use an OAG in the above combinations, we provide an additional 10mm spacer adapter in some kits to replace it.
A1-A3 (for 163M, 294M)
A1
A1: Connecting MPCC that requires 55mm BFL and M48 interface to Camera with Filter Wheel and OAG.
Note:
- If you only own CFW3M-SR whose BFL is 20.5mm rather than 17.5mm, this adapter combination can still be used, just remove the 3mm and 0.5mm adapters.
- If your MPCC requires a BFL different from 55mm, this adjustment can be made by selecting the appropriate spacer between the MPCC and the OAG. For example, an MPCC that requires 57.5mm can be used instead by adding a spacer ring or rings that add 2.5mm of BFL. to the diagram above.
- If you don’t use an OAG, you can use a 10mm spacer adapter in the adapter kits to replace the original position of OAG.
- Put OAG at the position next to the M48 Output to make both main cam and guiding cam focused.
A2
A2: Connect Canon lens with filter Wheel. You need to remove the filter wheel and the original connection interface of the camera and replace it with a new adapter.
A3
A3: Connect Nikon F Lens to Camera with Filter Wheel
B1-B3 (for 268M, 600SBFL)
B1
B1: Connecting MPCC that requires 55mm BFL and M48 interface to Camera with CFWL and OAG. B1 is standard accessories of QHY600M SBFL and QHY268M, so you needn’t purchase it if you’ve had the cams. If you own a CFW3M-US (which is 17.5mm) rather than CFW3L (21.5mm), you need to add another 4mm adapter and longer screws, which are also included in B1. Below shows two examples:
Note:
- If your MPCC requires a BFL different from 55mm, this adjustment can be made by selecting the appropriate spacer between the MPCC and the OAG. For example, an MPCC that requires 57.5mm can be used instead by adding a spacer ring or rings that add 2.5mm of BFL. to the diagram above.
- If you don’t use an OAG, you can use a 10mm spacer adapter in the adapter kits to replace the original position of OAG.
- Put OAG at the position next to the M48 Output to make both main cam and guiding cam focused.
B2
B2: Connect Canon EF lens to Camera with filter wheel
B3
B3: Connect Nikon F Lens to Camera with Filter Wheel.
Note: The current Nikon adapter used here is different from the 10mm adapter we used to provide. Now it has a back focal length increment of 12mm.
B4 for New 268C
From 2023, the top part of QHY268C will change to the shorter one just like that of 268M. In fact, you can get the “SBFL(shorter back focal length” version of 268C right now.
The previous 268c has a back focal length of 17.5mm, and since it cannot connect to the scope without CAA, so it’s actual BFL is 17.5mm+6mm=23.5mm. Now after the change, 268C’s BFL will be shorten to 14.5mm, which provides more spaces for a filter wheel drawer, or an electric CAA, or DSLR Lens, etc.
The new 268C adapts a new kit B4 which can best make use of the standard accessories. B4-2 and B4-3 share common parts from the necessary B4-1(for MPCC) .When you need to connect Canon or Nikon lens, you only need to get one Canon/Nikon adapter, not a “kit” like D2 or D3 anymore.
C1 (for 600M-PH, 600L)
Kit C1 is for connecting MPCC that requires 55mm BFL and M48 interface to Camera with CFW3L Only. C1 is standard accessories of QHY600M PH and QHY600L, so you needn’t purchase it.
Additional Resources