Hmm Just wondering

[leon]

Hmm Just wondering
Hi guys, I sent this question to a very experienced imager here on IIS, and although It was just a recent PM, I did not expect an answer just yet, so to my PM'ed person, please don't feel offended because I put this out there, I thought some different feedback could be helpful.

The Question being.

* In comparison of image quality, which one of these instruments would give the better image, and why please.

FSQ-106 or, Canon 500mm F/4.0L IS USM, or would they both be pretty equal in their performance.
I love my Tak, and it is crisp and clear, but would a 500mm equal it's performance.

Thank You.

Leon

[troypiggo (Troy)]

I'm a bit of an astro noobie, but my initial thoughts are that astro shots taken with lenses rather than scopes have diffraction spikes due to the iris of the aperture. Refractor scopes seem to have no diffraction spikes unless you put crosshairs etc over the end.

[Geoff45 (Geoff)]

You'd expect the lens to be better as it has more lens elements in its design. If they could get away with a doublet like the Tak, why would they bother with the extra expense?

[strongmanmike (Michael)]

That's a very good question and one I have had before too..?

I would expect the Lens to be much more expensive than the FSQ since it has a larger front objective and more optical elements?

Interesting

Mike

[gbeal]

I'll go out on a limb here Leon, I reckon the Tak will be better.
But the biggest problem I have with your question is, better for what. If astro is your desire then I believe the Tak will be better, but you don't actually stipulate this (do you?).
Gary

[jase (Jason)]

Interesting topic...

FSQ-106N,ED(EDXI&II) is a four element in two group design (two doublet Petzval), the Canon 500mm lens (wait for it) 17 elements in 13 groups! Serious amount of glass, but the quantity of glass has nothing do with this equation. Looking at the Canon 500mm lens at the business end i.e. where you attach the camera, max aperture is 52mm or typical filter size. This wouldn't be the image circle size. I would expect that to be less. Perhaps 48mm or so. This is similar to the FSQ-ED with either the optional Focal reducer or extender which is 44mm. However, natively (F/5), the FSQ has an image circle size of 88mm. Massive! If you were to put the lens on a large format camera, I'd expect to see considerable vignetting, though it would need to be something larger than the KAF-6803 chip that comes in at 38.6mm x 37.7mm. Technically the FOV would be illuminated but the drop of in light in the edges would be more severe. Light drop off on the FSQ with this chip is ~300 ADU - very little. Its difficult to get specifications on the colour correction for the Canon lenses. Given the high quantity lenses, I don't doubt one moment that they are world class, however it would be good to know. The new FSQ for example is corrected to 1000nm, well up into the IR range, designed to reduce star bloat. I'd also be very interested in how flat the field is across the image plane between the two.

At this stage, I think its difficult to draw a conclusion. I admire the wide field work lenses provide, but at fairly close focal length I'd say the FSQ has the edge. I wont be selling mine in a hurry (put it that way). Perhaps a more accurate test would be the Canon 400mm F2.8 and the FSQ-ED with reducer delivering 385mm F/3.6.