Hi everyone, I have been looking for some information about using barlows/focal extenders to achieve variable magnification for EAA with short refractors.
The idea is to use a barlow lens or focal extender to change the image scale in my EAA rig. This is going to be used with a variety of short refractors: F4-F6.2, 50mm - 80mm apertures. The max sensor size is 13.5mm.
The main question that I'm try to answer is to choose a barlow that can be used to achieve variable image scale, by changing the distance between the barlow and the camera. Theoretically all barlows provide a certain range for distance / scaling, but I don't know how practical is that in terms of image quality/aberrations. I'm looking for 1.25".
The barlows I have considered so far:
- TV powermate: pros: predictable quality; cons: constant 2.5x magnification regardless of the distance.
- GSO APO 2.5x: pros: reportedly good quality, reportedly variable magnification based on the distance; cons: unknown
- GSO 2x ED barlow: pros: nothing special; cons: 2-lens element, compared to above, couldn't find any reference about the magnification range based on the distance.
- Baader zoom barlow 2.25x: pros: reportedly good quality; cons: no user reports about distance/magnification.
- Baader Q barlow: advertised 1.3x, 2.25x dual magnification, assuming any values in between are achievable; cons: doesn't seem to match the quality of any of the above.
On a separate note: I understand the consequences of increasing the F-ratio, I'm OK with it. Currently I'm experimenting with my F12 mak for EAA, quite happy with it if expectations are set up properly.
It would be great if someone could share their experiences. Thanks!