Field Flattener question

[Anthonyexmouth]

Just added an altair astro 0.8 FF/R to my ED80. can someone tell me if the distortion in the corners is guiding error or the limitations of this flattener, would i have been better off with the SW .85 dedicated one?

[michael8554]

To my eyes the stars in the corners are elongated in the direction that means the spacing is too much - according to the diagrams I have seen here on SGL.

If the spacing was too close, the stars would again be elongated, but this time pointing away from the centre of the frame - according to those diagrams.

I've no idea how critical the quoted 55mm spacing is, but a 10mm T2 Canon adapter and 44mm Canon back focus would be 1mm under.

Michael 

[Anthonyexmouth]

7 minutes ago, michael8554 said:

To my eyes the stars in the corners are elongated in the direction that means the spacing is too much - according to the diagrams I have seen here on SGL.

If the spacing was too close, the stars would again be elongated, but this time pointing away from the centre of the frame - according to those diagrams.

I've no idea how critical the quoted 55mm spacing is, but a 10mm T2 Canon adapter and 44mm Canon back focus would be 1mm under.

Michael 

the altair site does say its made for a dslr and a 10mm adapter. hoping i havent made a mistake in buying it. 

[Anne S]

My Starwave reducer had a 10mm spacer fitted so that the dslr adapter bit gave the correct spacing. You don't need to add anything else. I had to remove it for ccd imaging as I have a filterwheel. 

[Anthonyexmouth]

this is the one bought. but the 0.8 version

[Anthonyexmouth]

Just checked and the top unscrews and takes 10mm of and reveals something like an m54 thread. 

When measuring spacing, where do you measure from and to? 

[Anthonyexmouth]

Am I expecting too much from this flattener? or have i set it up wrong?

i did email altair in the week but not had a reply, wondering if i bought the wrong one. 

[geordie85]

On 28/02/2019 at 15:32, Anthonyexmouth said:

Just checked and the top unscrews and takes 10mm of and reveals something like an m54 thread. 

When measuring spacing, where do you measure from and to? 

The measurement should be from the seneor to the beginning of the flattener. As you can't get to the sensor you'll have to find out how deep into the camera it is then add that to the measurement from the front of the camera to the beginning of the flattener. 

[Anthonyexmouth]

i measured from the sensor mark on the camera body to the first flat flange on the flattener, measured 54/55mm . maybe im expecting too much and the distortion in the corners is going to stay, or maybe something else is causing it

the top of the flattener does unscrew so should i be measuring from there or below that. 

[david_taurus83]

I thought the SW one was pretty much bob on? Any images I've seen with an ED80 at 0.85 the stars look good? Why did you go for a different one?

[Anthonyexmouth]

2 minutes ago, david_taurus83 said:

I thought the SW one was pretty much bob on? Any images I've seen with an ED80 at 0.85 the stars look good? Why did you go for a different one?

id read that it was a slightly better quality FF, that and it meant i could afford a click lock which makes framing easier. 

[david_taurus83]

I'm in the same boat I suppose. I have a WO Flat6A 0.8 flattener which induces a bit of tilt and a Hotech SCA 1.0 flattener which doesnt work at the required 55mm back spacing! I've given up worrying about it now as it can ruin a good clear night trying to iron it out. My approach now is to image a target, process and throw the image out there. If it needs spacing adjustments then I'll add a bit more and image a target again the next night. Hopefully I might find that sweet spot! But I'm not going to dwell on it. After all, amateur with amateur kit.

[alacant]

Hi. The flattener needs to be closer to the sensor. Are you sure you have a 10mm adaptor? What you are seeing would happen if it were more than 10mm. Or just accept it and correct it in software. Cheers.

[Anthonyexmouth]

11 minutes ago, alacant said:

Hi. The flattener needs to be closer to the sensor. Are you sure you have a 10mm adaptor? What you are seeing would happen if it were more than 10mm. Or just accept it and correct it in software. Cheers.

yeah, the adapter is 10mm. when measured from the sensor plane symbol on the camera to the flat on the back of the flattener its 54/55 mm. definitely within 1mm of 55mm. unless i should be measuring to the point behind the m42 adapter on the flattener

[michael8554]

Point 1 or point 2 - another frustratingly vague spec from the makers.

Try 2,  both myself and alacant agree it should be closer.

Michael 

[Anthonyexmouth]

when i remove that back bit i'm left with a what looks like an m54 thread. nothing i've seen is any slimmer to convert it down to m42 so not gaining anything. 

[alacant]

Hi. Are you sure it's m54? If it's n48 then a wide n48 t adaptor (with the M42 unscrewed) would get you there. 

OTOH, (keeping the M42 adaptor screwed on) it looks like you're gonna need a low profile adaptor instead of the 10mm. 

Yeah, it really isn't clear. The Baader is the same but at least they send you a diagram with and without the M42 adaptor...

HTH.

[Anthonyexmouth]

Not easy to see, but certainly not m48. Just braved the wind and rain to get the camera off the pier. 

 

[Anthonyexmouth]

Well this arrived this morning. Let's see if reducing the spacing helps. If course it'll be cloudy until June now. 

[Anthonyexmouth]

OK, after weeks of cloud i got out with the new low profile t ring fitted

heres the result. can anyone more experienced tell me if this is looking as it should.

[Thalestris24]

Hi

Um there are distortions in all the corners and along the bottom, I'm afraid. Spacing + tilt? Remember you need spacing to within a mm and allowance for any filters.

Louise

[Anthonyexmouth]

Would my clip in filter be causing any issues? 

the original t ring measured the correct 55mm but the feedback was it was too far away, hence the low profile t ring. 

[Thalestris24]

1 minute ago, Anthonyexmouth said:

Would my clip in filter be causing any issues? 

the original t ring measured the correct 55mm but the feedback was it was too far away, hence the low profile t ring. 

It might. I would try without the filter and a standard t-ring... But if there is some tilt you'd need to sort that out first really. What does the spacing measure with the low profile t-ring? These things can be a real pain to sort out...

Louise

[Alien 13]

I cant comment on SW scopes but found that the spacing on my WO one and FF needed to be within 0.1 mm or better, the final solution was 54 .12 mm.

Alan

[Anthonyexmouth]

can't remember off the top of my head. doesn't help not knowing exactly where i should be measuring to on the flattener. 

off topic but spent the cloudy time doing a bit of tidying of the wiring and popped an Amazon Alexa enabled faceplate socket in the workshop, can now tell alexa top turn the telescope on and i don't have to open the workshop up. Its like living on the Enterprise.