"T shirt" flats

[ollypenrice]

On 01/12/2018 at 09:30, Demonperformer said:

OK, I think this could be a case of my OCD exerting its authority. When people tell me flats have to be taken with everything exactly the same as used for the lights, I tend to cling on to the word exactly in a way that would make a limpet appear weak-willed.

The subtraction idea certainly seems to be a reasonable way forward, and I may try that with the 224 flats I did above ... if I can work out how to do it in GIMP!

Thanks.

I think it's a good idea to take 'exactly' seriously at first, though clearly you can't shoot a set of flats between fine focus changes - or you could, but to do so would be potty.

In scandalous disregard of 'exactly' I use a master bias instead of a dark-for-flats and (tell nobody) I often use a luminance flat for all filters.

lly

[michael.h.f.wilkinson]

I have found that in many cases the most important thing flats correct for are dust bunnies close to chip (usually on the filter or glass window immediately in front of the chip). There is of course the vignetting of the optical system, but that is often far less severe, and doesn't change much with e.g. camera rotation, or filter change, if the filters are far enough from the chip. For some lunar work I have studiously collected flats for L, R, G, B, and IR, only to find that it really doesn't matter which flat i use of these five. I have even been able to use flats taken a few sessions ago with impunity. I do try to make the flats every time, but sometimes conditions conspire against this, and then all you can do is use the latest flats taken with the same camera-scope combination

[ollypenrice]

48 minutes ago, michael.h.f.wilkinson said:

I have found that in many cases the most important thing flats correct for are dust bunnies close to chip (usually on the filter or glass window immediately in front of the chip). There is of course the vignetting of the optical system, but that is often far less severe, and doesn't change much with e.g. camera rotation, or filter change, if the filters are far enough from the chip. For some lunar work I have studiously collected flats for L, R, G, B, and IR, only to find that it really doesn't matter which flat i use of these five. I have even been able to use flats taken a few sessions ago with impunity. I do try to make the flats every time, but sometimes conditions conspire against this, and then all you can do is use the latest flats taken with the same camera-scope combination

Agreed. In my permanent setups a set of flats will sometimes work for six months.

Olly

[Stub Mandrel]

Has anyone done a comparative test such as Peacocks vs Superdry?

I've found that dust bunnies = need new flats. Scrupulously clean sensor* + always align camera the same = flats last until next collimation.

 

* the gel square on a stick type sensor cleaners work wonders.

[tooth_dr]

11 minutes ago, Stub Mandrel said:

Has anyone done a comparative test such as Peacocks vs Superdry?

Or the freshly ironed versus the one you were wearing when you went out in the morning to pack up.