Hi Glen,
The 100mm in my case is from the glass, which is 4mm inside the housing. see image1 below and the 61.5mm according to Moravian website is from the sensor to edge of OAG see image 2 below. I can't find any mention of cover glass or if its included in the specs or not.
Quote:
Originally Posted by glend
Yes this is known as the "Rule of 1/3rds". Each 1mm of glass lengthens the focal length by 0.33mm. You don't actually add the filter thickness as it sits in the light path, only the optical effect of it being there. Don't forget that any camera sensor compartment cover glass will also enter into calculation.
Also note thatsome flattener backspacing is measuredfrom the shoulder of the flattener, not the end of the threaded section, better check on that.
|
Hi Mark thanks very much for that I obviously would have gotten the wrong lenght. Its a F7.
Rereading the manual sugests a +/-1mm to obtain a flat field, so mustn't be super critical.
Quote:
Originally Posted by markas
John,
On your figures, you must ADD the 0.33mm for the filter glass to the adapter thickness - ie the adapter thickness would be 34.83mm.
As to how critical it is, it depends on the telescope f ratio. For a very fast system it can be super-critical.
Mark
|
Cheers