new tecnosky 4 element 0.8 flattener

[alacant]

Hi everyone

I'm hopeless with refractors. Has anyone experience of these?

What bf should we use for a 72ed -fl 432mm- and is that with or without the 8.5mm ring pictured?

TIA

 

Edited June 23, 2023 by alacant
tec tech

[fozzybear]

Here you go

[alacant]

Thanks

Is the 55mm with the supplied 8.5mm collar in place?

TIA

[fozzybear]

21 hours ago, alacant said:

Thanks

Is the 55mm with the supplied 8.5mm collar in place?

TIA

the details i provided is the backfocus requirements for the 72ED you would need to check the flattener specs. So from the neck of the drawtube to the sensor is 134.4mm

eg using a DSLR wirth 55mm backfoucus your need to add 79.4mm from the edge of the focuser either with a FF or extensions or a combination, and visa versa with a CCD camera with a filter wheel and what ever else you have to to make up the 134.4mm if that makes scense 

Edited June 20, 2023 by fozzybear

[alacant]

Thanks again

Unfortunately, it's the backfocus distance I'm missing. The three element version came with suggested backfocus distances. These depended upon the focal length of the telescope in which they were deployed. I copied those distances here:

The new version has nothing; I was handed a box devoid of any hint of instruction. Maybe the best plan is to assume it's the same as the old version and begin with a backfocus of around 65mm, point at Cygnus and hope it doesn't take all night to nail it.

Cheers

Edited June 24, 2023 by alacant

[fozzybear]

5 hours ago, alacant said:

Thanks again

Unfortunately, it's the backfocus distance I'm missing. The three element version came with suggested backfocus distances. These depended upon the focal length of the telescope in which they were deployed. I copied those distances here:

The new version comes in a plain box devoid of any suggestions or explanation. Maybe the best plan is to assume it's the same as the old version and begin with a backfocus of around 65mm, point at Cygnus and hope it doesn't take all night to nail it.

Cheers

Ah Ok I misunderstood what info your where looking for hopefully you can sort it out. 

[alacant]

Hi everyone

We began the trial and error last night. Forget the customary 55mm.

We got as far as 66mm ff to sensor.. It's tilted -the darn flattener has an undercut- so it's useless with a compression ring. Have been trying unsuccessfully to find the whereabouts of the original collar without the ring. At least the stars seem roundish.

Tilt apart, it seems to be an improvement over the three-element, false colour at the extremities has gone and the stars are well controlled. I don't know if I have the patience to do another session of screwing-unscrewing-dropping-fumbling,

Anyway, here's what it's like over aps-c. It plate solves to 345mm.

 

Edited June 24, 2023 by alacant
66

[david_taurus83]

Ah! Alacant! Champion of the reflector, welcome to the maddening world of refractor back spacing! Lol

Seriously though, I have tried them all, WO, OVL, Planostar, Telescope Express, HoTech etc None of them ever gave me perfect stars in the corners or sides. The closest was the WO reducer as they gave specific measurement for different scopes. As you've found above, pick something you are happy with and leave it alone! 

FYI, the best flattener to date is the specific one made for my Esprit 100, nice round stars across the frame with both my 533MM and 2600MC. Best coma corrector for my 200P is the TS GPU.

Edited June 24, 2023 by david_taurus83

[happy-kat]

This thread opened my eyes to other things to play with in Siril, cheers