WO ZS71 + Flat6 spacing

[Demonperformer]

I have been trying to work out the correct spacing I need to use for my ZS71 + Flat6 reducer/flattener and my starting point is this FLO page.

Now this starts by saying that the "Lens to chip suggested distance: 55-57mm". However, in the diagram with the EOS chip, the distance from the centre of the lens to the chip is 6.68+68.32 = 75mm. And in the picture below that, the distance is given as 79.52mm. (I don't see how the FF knows how to change the light path, or even can, depending on which chip I am using. Also the diagrams are labelled Flat6A, rather than Flat6 - is that significant?)

OK, down to specifics.

I will be using the 1600MM camera.The one essential piece of equipment is going to be the OAG. The distance from the back-lens in the FF to the edge of the OAG is about 35mm (the breaks down into the distance from the lens to the end of the FF is 22mm and the OAG body is 13mm - this includes the very narrow thread on the camera-side of the OAG). The distance from the camera to the chip is 17.5mm (I could reduce this to 6mm, but then I would not be able to add a filter, which fits in the connector). This gives me a total of 52.5mm. So, I would appear need either a 2.5-4.5mm spacer (if 55-57mm is correct), or a 22.5mm spacer (if 75mm is correct) or a 27mm spacer (if 79.52mm is correct).

I currently have a 15mm ring and a 30mm ring (and some larger ones), so I am likely to need to buy something new to get it right, but would prefer to buy the right one rather than buy one at random and hope!

Could someone who knows about these things please check my figures and advise what size extension ring I am going to need to get it to focus properly.

Thanks.

[SkyBound]

That information is very contradicting indeed, maybe drop FLO an email and ask, as it will confuse everyone.

i was under the understanding that the WO FF/FR worked at 55-57mm and that's what I have used mine at in the past with perfect results

[SkyBound]

I don't think you can get spacers under 5mm to leave at 52.5 and give it a try...probably better to be a bit under the 55-57 rather than over it..

[Demonperformer]

Thanks for the response.

If I had bought them, or even one of them, at FLO then I probably would have gone back to them and asked. But as both scope and reducer were bought elsewhere (second hand) I feel a bit awkward going to them for advice on how to use gear I got elsewhere. I know they are nice guys, but they are a business, after all.

I have been thinking, since starting the thread, that, even though I don't have a distant object upon which I can focus, I could still set it up and try it on one of the local trees. True the exact focus point would be different, but if I can focus on a tree, it is a fair bet that I am within the right ball-park for focussing astro-wise. So might give that a go and see what I get.

Thanks.

[Oddsocks]

13 minutes ago, Demonperformer said:

I have been thinking, since starting the thread, that, even though I don't have a distant object upon which I can focus, I could still set it up and try it on one of the local trees. True the exact focus point would be different, but if I can focus on a tree, it is a fair bet that I am within the right ball-park for focussing astro-wise. So might give that a go and see what I get.

I'm afraid setting up in the daytime will not help you with flattener spacing, the central ray will allways be in focus irrespective of distance ( within certain limits of course ). 

Changes to the spacing affect the degree of curvature correction and it will be very hard to judge this on a terrestrial object, you need to be focussed at infinity and be looking at a field of point sources to determine if the curvature correction is over, under or optimal.

No reason not to try of course but I wouldn't make a spacer purchasing decision based on a daytime assessment.

It is worth an email to W.O. For clarification. He is not the quickest at replying but when I had W.O. questions in the past he always replied within a week.

 

[Demonperformer]

That would explain why, no matter how long the extension ring I use, I can still get it to focus ... "What's all the fuss about?", me wonders ...

Thanks

[Oddsocks]

If it helps here are the links to the older flat 6 spacing documents.

For the older Z71 at F6 the distance lens to CCD is 70.5mm +/- 1mm which seems a good place to start.

( the flat 6 was designed before the ZS71 which is probably why no data published specifically for that combination, the flat6a came later and tuned specifically for the newer series of telescopes )

http://www.williamoptics.com/accessories/P-FLAT-F6.PDF

http://www.williamoptics.com/accessories/flattener6_spec.php

 

 

[Oddsocks]

23 minutes ago, Demonperformer said:

"What's all the fuss about?", me wonders ...

Well, if the distance is wrong you don't correct the coma, or make it worse, spacing tolerance is tight and becomes tighter the faster f. ratio the telescope is.

If you are using "T" mount and have the space then the Baader variable spacing "T" adaptors take a lot of the pain away by allowing to fine tune the spacing.

https://www.firstlightoptics.com/adapters/baader-varilock-29-lockable-t-2-extension-tube.html

https://www.firstlightoptics.com/adapters/baader-varilock-46-lockable-t-2-extension-tube.html

 

[Demonperformer]

Thanks for those docs.

That gives me:

Lens to OAG: 35mm & nose to chip: 17.5mm; total 52.5mm

70.5 - 52.5 = 18mm +/- 1mm

I have a 15mm extension tube, so presumably one of these is what I need to buy.

[Demonperformer]

1 minute ago, Oddsocks said:

If you are using "T" mount and have the space then the Baader variable spacing "T" adaptors take a lot of the pain away by allowing to to fine tune.

Unfortunately, I don't think my figures would allow for even the shorter of these.

Thanks.

[Oddsocks]

24 minutes ago, Demonperformer said:

Thanks for those docs.

That gives me:

Lens to OAG: 35mm & nose to chip: 17.5mm; total 52.5mm

70.5 - 52.5 = 18mm +/- 1mm

I have a 15mm extension tube, so presumably one of these is what I need to buy.

With your current spacer and proposed TS ring that is the closest you would get, and if your spacing figures are correct would probably be fine, if you needed to fine tune to a shorter spacing then you would need a different combination of primary spacer and additional rings, I would try your suggestion and go from there.

(If the spacing is out the effect of over or under correction is related to the size of imaging field, you can be miles out with an APS sized detector and not see anything but swap to a full frame sensor and the wrong spacing shows clearly around the edges of the field)

 

[Demonperformer]

Not sure what those detector sizes are, but this camera is '4/3" CMOS, 21.9mm diagonal'.

Thanks.

[Oddsocks]

13 minutes ago, Demonperformer said:

Not sure what those detector sizes are, but this camera is '4/3" CMOS, 21.9mm diagonal'.

4/3" format is a little smaller than APS.

https://en.m.wikipedia.org/wiki/Image_sensor_format

http://theonlinephotographer.typepad.com/the_online_photographer/2016/01/camera-sensor-size.html

 

[Demonperformer]

Right, found a 3mm ring on ebay that is less than half the price of getting one from TS (when you include the delivery), and it should be here on Monday. Never particularly confident about ebay, but at £7.90, I can't lose an enormous amount.

[knobby]

The 55-57mm lens to chip is common assumed distance from a SLR lens flange to the imaging sensor.

Therefore the spacer Flo recommend will achieve the figure w o suggest.

Not applicable to your ASI 1600, go with whatever spacers you need to achieve w o spacing.

[Jokehoba]

I don't have the exact details to hand but to connect my WOZS71 + 0.8FF to the ASI1600, I have added 50mm (40mm plus 10mm M42/0.75) extension. Took me a while to appreciate that the 6.68mm measurement is mandatory in all configurations. The FLO/WO diagrams are confusing. The difference between the 75mm and 79.52 is the part of the T-ring that is recessed in the camera body when attached.

So I have:

FF     +  extension + ASI1600

6.68 + (10 + 40)  + 6.5  = 73.18mm

Not perfect but seems to be OK. I did buy some cheap (sub £10) M42 extensions from eBay but they turned out not to be 0.75 pitch so didn't thread properly. Hope yours ar the right type.

[Demonperformer]

Is this with the older Flat6 or the current Flat6A? I ask because the distance from the centre of the lens to the edge of the FF is 22mm on mine. Thanks.

[Demonperformer]

21 hours ago, Jokehoba said:

I did buy some cheap (sub £10) M42 extensions from eBay but they turned out not to be 0.75 pitch so didn't thread properly. Hope yours ar the right type.

Arrived today (24 hours). And it is the right pitch (at least, it screws on and off everything quite happily with no 'binding'). Happy to recommend them.

[Jokehoba]

Thanks @Demonperformer. The ones I'm now using are the correct type - just cost three times as much!

[hiroshiman]

Cheers guys,

I am very interested by this topic. I bought a used ZS71 and just ordered the Flat6 (I though I had ordered a Flat6a...) at FLO and I am of course asking myself the same questions as you do. After looking around on forums I read that the distance 55-57 should be from the shoulder of the Flattener (where is the M42 thread I guess) to the chip. Is that right ? Since my first language is french I struggle a bit when I read these posts about the spacing. I am using a Nikon and the distance from the flange (ifI understand the word flange) to the chip is 46.5 in it so I guess I just need 10mm more. I don't know how thick are these T Rings (the only thing tha annoys me with FLO, not enough details on their products). Does anyone own one of them?

Sorry because the answer might just be up there but as I told you, it is a bit difficult to feel comfortable with technical details when they're shared in another language.

Napoleon used to say that a good drawing is better than a long speech. Does this look right to you?

Thanks

[Demonperformer]

Well, I reckon the distance from the lens to the flange is 16mm (the thread is 6mm, making the 22mm I mentioned in my earlier post). If I add 16 to 55 that gives me 71, which is certainly close to the 70.5 +/- 1mm, bearing in mind that I am measuring the internal distance of the FF with a cocktail stick!

In the end, the only way I will know for certain if I have got it right or not will be when I am able to get out and use it ... which is due to be about 2018 judging by the forecast!

HTH

[hiroshiman]

I don't like cocktails but I will certainly invest in cocktail sticks, I didn't know it was part of the casual astrophotographer gears  

Anyway, I'll keep following your post, and if anyone want to jump in about the T Rings, don't hesitate.

See you in 2018

[Demonperformer]

If you intend purchasing from FLO, I would drop them an email - they are very knowledgeable and helpful.

[Alien 13]

I have the ZS71 with FR/FF 6 and have used it with both Canon and Micro 4/3 cameras and in both cases a STD T ring for your particular camera will get you the correct spacing I.E. for Canon the flange to chip distance is 44 mm the T adapter is around 12 mm thick so this gives a total of 56 mm which is the specified spacing from WO.  If you want to fine tune this distance you can add delrin washers, think FLO sell a spacer package for this purpose.

Alan

[hiroshiman]

Hi guys.

So I contacted FLO and talked with James. He has been super nice and helpful. His answer confirmed what Alan stated above.

"I will check the T adaptor for you - the thickness of these can vary slightly depending on the manufacturer but are generally based on filling 55mm up (the flange to sensor distance of a DSLR + the thickness of the t adaptor. Spacing wise with flatteners and the like the distance is usually given from the thread on the flattener, so if the lenses are inside by a few cm it doesn't matter - but you've already worked that one out "

I just spent a lot of money on their website and will not hesitate to do it again (I'll have to save a little...)

A+