AP with a TMB92 APO?

[RayGood]

Is there anyone out there who does AP with a TMB 92-SS or -L?

I wondereing whether AP Prime focus with an APS sized sensor could be done without a field flattener. On S&T review, the author mentioned a 15mm centre circle that had no field curvature. Well, that pretty much at least, covers the height of an APS sensor of height 14.8mm (for the cannon 1000D). The width of this sensor is 22.2mm. So that, minus 15mm, equals 7.2mm. Now only half of that (3.6 mm) on either side of the width side will be exposed to the beginning stages of field curvature.

Now, I am only a beginning AP, as some of you already now, but I wonder whether this small amount of field curvature would be noticeable to me or not. Probably be best if I could ask someone who actually uses the scope for AP.

I had tried contacting Otto (the author of the CN review for the TMB 92_L) but his e-mails are returned. Not sure his address is working anymore.

Anyone elese take pictures with this scope?

Or know anyone on SGL who has, that might know?

[ollypenrice]

It is usual to take the diagonal as the measure (Pythagoras) so as to equate with the quoted image circle.

Olly

[RayGood]

Sorry, Olly. What you said there went right over me. May I ask, what did you mean by your statement please?

[ollypenrice]

The diagonal measurement of the chip, corner to corner, will compare with the diameter of the image circle quoted for your scope like-for-like. If you don't have that diagonal measurement you can get it from Pythagoras. Or of course you can just measure it from a quick scale drawing using your chip height and width.

Olly

[RayGood]

Thanks Olly. The diagonal of the sensor is 27mm, rounded to the nearest whole number.

Givern a 15mm diameter circle of flat field, do you think field curvature would be pretty noticeable to a beginner astro photographer with a sensor diagonal of 27mm?

[ollypenrice]

Thanks Olly. The diagonal of the sensor is 27mm, rounded to the nearest whole number.

Givern a 15mm diameter circle of flat field, do you think field curvature would be pretty noticeable to a beginner astro photographer with a sensor diagonal of 27mm?

Well, yes. But suck it and see. If you have a big chip you can just crop it. Even an expensive CCD like our Atik 4000 only has a 15mm square chip so a DSLR can throw some away! I exceed the manufacturer's flat field of our TEC140 but it won't keep me awake at night. The corner stars are as near as dammit. You just have to see what you can live with. I can tell you a really nasty, unethical star-rounding Photoshop technique if you like...

Olly