A new SHG using a cheap 300mm f5.6 lens

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thesmiths
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A new SHG using a cheap 300mm f5.6 lens

Post by thesmiths »

One version of our "wide-field" SHG used a Canon 300mm f4 L IS lens as the "telescope". This didn't achieve as good results as I had hoped, despite it being a very high quality camera lens. Given that it has autofocus and image stabilisation built in, I hypothesised that perhaps it just had too many lens elements (I think there are 15) and that this might create some problems.

Canon EF 300mm f4 L IS lens -- possibly too complicated. 15 elements in 11 groups. Blue elements are UD glass. Internal focusing.
Canon EF 300mm f4 L IS lens -- possibly too complicated. 15 elements in 11 groups. Blue elements are UD glass. Internal focusing.
diagram.gif (4.45 KiB) Viewed 216 times

So instead, I went in the other direction and tried out a very cheap 300mm f5.6 generic vintage lens. This lens apparently has only 4 elements so in some way is more like a simple telescope. My initial experiments show that this simple cheap lens does seem to work a bit better than the expensive modern Canon lens. The cheap vintage lens is also considerably lighter (560 vs 1190 gm) and has a very nice built-in helical focuser, as well as a very convenient tripod adapter.

SHG using inexpensive vintage optics
SHG using inexpensive vintage optics
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The "telescope" is a 300mm f5.6 Prinz Galaxy, the collimator is a 100mm f4 Palinar (also a simple, cheap lens with a very nice helical focuser), and the camera lens is a Rodagon 135mm f5.6 enlarging lens mounted on a BPM bellows to enable focusing. The diffraction grating is a 50mm x 50mm 1800 l/mm ruled grating from Thorlabs and the slit is 20 micron wide and 3mm long, also from Thorlabs.

CaH image at 300mm, 4 Dec 2021
CaH image at 300mm, 4 Dec 2021
121558_shift=0_clahe.jpg (87.9 KiB) Viewed 216 times

The camera in this case was an ASI 290MM. A Hoya NDX4 neutral density filter was mounted in front of the 300mm lens. The image was taken at 4ms and gain of 22, with a scan speed of 25x (in DEC). This is a relatively low-resolution set-up but there is clear evidence of the filament in the southern hemisphere. This filament is only weakly visible in H-alpha and normally not visible at all in Calcium.


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Re: A new SHG using a cheap 300mm f5.6 lens

Post by Montana »

I was just going to say that I can clearly see the filament that Ken imaged in his post. Lovely work!!
:bow :hamster:

Alexandra


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