MORE Takahashi Questions

[adman]

Can one of our resident Tak experts please help. I just received an order that I am not sure is correct.

I am trying to connect my Canon EOS to my FS-60CB, and looking at the system chart for this scope - the configuration that includes the flattener is what I am hoping to acheive - its the 3rd from the bottom.

I ordered a wide T-mount part (number 33 on the chart) Part No. TKA20233, and I don't think that what i got is correct, or I ordered the wrong Part Number - can someone enlighten me please. I have attached a photo of the part I received.

Thanks
Adam

[Paul Haese]

That is not a wide T mount fitting. I think that is part of the adapter that you need to place the wide T on.

[adman]

I had a wide T-mount that I used with my ED80 reducer - but that got sold with the scope. Will any wide T mount do, or do I have to get the Takahashi one...?

[Exfso]

Adam, Paul is correct, here is a photo of mine for the Toa130 and a 40D. sorry the image is a tad blurry, but I think you can see that the part you got fits into the T adapter and is locked down by the grub screws on the T adapter.

Adam, I have added the image of the T ring from the Bintel shop, this is what your piece fits into.

[JohnG]

The part you have got is the correct part for the FS-60, you should have specified that it was for an EOS camera, the part then would have come with the correct EOS ring already attached.

I would say that you are going to have to order the EOS ring, only thing is that I don't know if it is a special size or not to suit the Tak Wide T-Mount. Note that this is a special size for the FS-60.

The order is then CAA, SD Ring, Flattener then Wide T-Mount.

Cheers

[adman]

ahhh - yep it all makes sense now - I might be able to remove that part from my exisiting adapter and replace it with the Takahashi one - will have to check when I get home..

Cheers
Adam

[keni]

Hi Adam,
I'm sure the guy who bought your old scope will let you borrow the adaptor to try on your new setup.
I believe he's very easy to get along with........:rofl:

Cheers,
Ken.

[Exfso]

Adam, I can confirm the T ring shown on my post from Bintel, does fit my TOA130 setup as shown. I bought a spare yesterday as the original was getting sloppy.

[adman]

Thanks Ken! That might be handy before I go and order something that is bound not to be the right one :rolleyes:

Maybe on the weekend?

Adam

[adman]

Thanks Peter - would you please be able to measure the diameter of the opening on the bayonet part that my adapter would fit into. I'm not sure that they would be the same for the 130 and the 60...

The adapter in my picture above is approx 52mm across the camera end and 60mm across the scope end....

Cheers
Adam

[Exfso]

Adam, the diameter that the tak part fits into is 52.2mm measured with a pair of calipers. The actual diameter of the tak "male" ring is 51.5mm measured with the calipers, so this gives 0.5mm play for the grub screws to take up. The diameter of the threaded part that screws into the scope(CA35) is 53.7mm. So it appears to me as though all you need is the part which I have photographed which is available from Bintel.

[RickS]

Adam,

I have a wide T-mount adapter for my FS-60CB and Nikon somewhere. I can go for a hunt and find it if that's any help. It did come in two parts and I had to fiddle around to put it together.

Cheers,
Rick.

[adman]

Thanks Rick - I'm sure you will have the same part as I have pictured above, but a different bayonet obviously...

I have screwed the ring to the scope, but don't have the bayonet part :sadeyes:. Ken has offered to let me have my old one back temporarily to see if it fits. Thanks for the offer though!

I have also emailed Bintel with pics/measurements (see new pic added in original post (http://www.iceinspace.com.au/forum/attachment_browse.php?a=91448)) to see if what they have will fit.

Cheers
Adam

[Exfso]

Adam, the 52mm is the critical one to fit the T ring for the camera. Mine is 51.7 and it fits the Bintel T ring perfectly. There is just enough play so that the grub screws take it up. I am 100% sure the Bintel one will fit.

[adman]

Well - looks like I sorted it out....

I was labouring under the misapprehension that the 60mm outer diameter of my ring had to fit completely inside the bayonet part of the T-ring - but the short 6-7mm lip on the scope end looks like it is important for the distance from the flattener to the sensor - so it is meant to sit out of the T-ring.....duuuhhhh!

So yes Peter you were completely correct. It even fit the t-ring I had for my MPCC.

Thanks to all who helped - including the bloke at Bintel!

Adam

[adman]

Well, it seems it was only kind of sorted out...

I took some images with this at Ten Chain Hill on Saturday night (between predicted and actual showers of rain ;)) and even with the flattener I am still getting way too much coma - see attached...

So, I have 2 questions:

1. in the system chart attached to the original post, the configuration third from the bottom shows what I interpreted to be an optional "SD Ring", whose function is a little uncertain, but seems to give you a closer minimum focusing distance. Would the presence or absence of this SD Ring affect the amount of coma?

2. The T-ring i used is the only thing in the setup that is not 'kosher' Takahashi gear. I would imagine that the thickness of the T-Ring plus Tak adapter (shown in original post) would be more crucial for coma - can someone please enlighten me?

When I ordered the wide t-mount, the actual bayonet part was accidentally not included with the shipment - but is on its way to me as we speak...

Adam

EDIT - the three images below are from left to right
1. A crop from the top left corner
2. a crop from the centre
3. the original image - jpeg'd and reduced to 25%...

[Exfso]

Adam, if you are using the refractor which I gather you are, you should not be getting coma. More than likely you have some sort of field rotation. If the stars are elongated in the same direction across the whole image I would say this is what you are getting. You have a flattener in the system and this should stop any peripheral elongation. I am getting something similar at present and have narrowed it down to my all up weight being a tad too much for my G11. My guiding is very good. Not sure if you mentioned your guiding, but make sure the clutches are not slipping as I have found this can cause "eggy" stars as well.

[DavidTrap]

Hey - you saw the rain coming on the weather radar too!!! I can't help it if it disappears 2km down the road!! :P

Peter - I saw the original image on the screen. The "egginess" was radial, not circular, so I don't think it's field rotation. The tracking graph was pretty good too.

My hunch is something to do with spacing. I'll see if I can track down the relevant webpage with Tak reducer spacings - I found it recently when trying to order some custom adapters.

DT

[DavidTrap]

Here is the document I was thinking about. Not sure if it has the appropriate distances for your scope.

DT

[adman]

Thanks Peter. I shouldn't have used the term 'coma' - I am just used to using it when referring to my newt. Tell you the truth - I don't even know what the hell you call it when you get it from a refractor - spherical abberation? off-axis distortion? . Anyway it's what you're trying to get rid of by using a field flattener on a refractor.

The eggy stars are in a radial pattern. You can see from the centre crop image that the stars are reasonably round (please ignore the noise from my 550D at 30 degrees C), the crop from the top left is representative of the other corners - the distortion all points towards the centre of the image. So definitely not guiding/clutches or field rotation.

Adam

[adman]

Thanks David - nope - no FS-60 distances on there....:sadeyes:

Adam

[adman]

I reckon its that dodgy iPhone 4 - newfangled technology...!

[Tandum]

Adam I used this page (http://www.optcorp.com/product.aspx?pid=10227)for distances.

It says, The 56mm back focus is measured from the rear of the threaded end of the reducer/flattener rather than from the shoulder.

[adman]

Thanks Robin - just so I get it right - that means 56mm from the rear of the threaded end of the flattener to the Canon sensor plane??

By the way - what a silly place to measure from - once its screwed in place - you can't see the rear of the thread....:P

Adam

[Tandum]

I'm not sure if the 44mm they quote for canon sensor distance is to the glass on the sensor or to the sensor silica itself and that glass is normall 1.5 to 2mm thick. I'm sure the real tak adapters would put the distance spot on. But the 56mm will be to the canon sensor so the adapters should be 12mm plus the flattener thread depth I guess.

I think my distances are out by a little as I'm using adapters off ebay to cobble my filter wheel to the flattener. I think it shows up here as my normally parfocal filters not being parfocal, they are all slightly out. L&R&B are very very close but not exact while G definately needs refocusing and being around F4 the focus point is very narrow.

[adman]

thanks Robin,

by my measurements, I am only about 1mm out. Would this be enough to give me the stars in the pics above??

The T-Ring + Tak adapter is 16.0mm thick and the flattener thread screws into this by 5.0mm - which gives a net of 11mm - add this to the 44mm for the canon sensor distance gives 55mm....

I will have to wait until the genuine kosher Tak part arrives to find out.

Cheers
Adam

[Tandum]

I dunnno. Here's a heavy crop of top left from my last image. Stacking is a bit suspect and green is bloated.

[RickS]

Adam,

I just took a close look at my last pics from the FS-60CB with flattener and Nikon DSLR and they look pretty good in the corners. I've never checked the back focus distance to see if it's accurate, but I guess it is. I got my adapter from Peter Tan. If you want me to measure anything or send you some images let me know...

Cheers,
Rick.

[adman]

Thanks Rick - if you could post an image with a crop of one of the corners that would be really helpful.

I also ordered the adapters from Peter - the Tak T-Ring didn't find its way into the shipment though - he is sending it with my next batch of stuff. Should be here any day.

I'm not sure whether there is any point measuring your gear if it is Nikon, unless the flange/sensor distance happens to be 44mm also??

Cheers
Adam

[adman]

I've just read that the sensor distance on Nikon is 46.5mm, so by my reckoning, on your setup, the distance marked 'a' on the diagram attached should be 14.5mm. On mine I think it should be 17mm, but I currently have 16mm...

Adam

[RickS]

Adam,

Here's a corner crop image.

Cheers,
Rick.

[RickS]

Let me see if I can find the hardware in my office pile 'o crap. I'm still getting things back in order after a long time exercise with our builder to find and finally fix the water leak in my subterranean abode...

[adman]

well - they are a damn sight better than the stars in mine.....

thanks for that.
Adam

[RickS]

Hey, it's a Nikon. I know all the Canon folks have the jump on me for astrophotography so it's nice to feel slightly superior for a few nanoseconds, even if only by accident :D

[adman]

well - I was able to whip the scope and mount out for a few short trial exposures the other night. I got the new T-ring, and I don't think it has made much, if any, difference. I think it added maybe an extra 0.5mm - so now I think my flattener to sensor distance is 55.5mm - in theory only 0.5mm out.

I think what I am going to have to do is unscrew the adapter a little to see whether the extra distance will help - although it will introduce its own problems with a bit of sag leading to the sensor not being perpendicular, it might show me whether I am heading in the right direction...?

Any other ideas?

Cheers
Adam

EDIT - the image is a crop again from the top left

[adman]

how good was last night in Brisbane?!! (if you don't count the lack of sleep :P)

it gave me a chance to fiddle around with spacings etc with the FS-60 flattener, and it was one of those nights where everything just worked :D. Guiding was just set and forget, everything balanced well, despite it being a last minute SBS job cobbled together from bits lying around, and any adjustments to balance, PHD settings etc did just what I wanted them to, not to mention it was cloud free....maybe there is a god...:shrug:

Anyway the good news (as you can see from the pics below) is that I have got the spacing right and am getting a nice flat field (the crop is from bottom left). The bad news is that I had to unscrew the T-Ring from the scope slightly to get it right, and now its just flopping around in the breeze...In the end, the difference between my last pic I posted and these was about 0.7mm (I bought myself a better set of vernier calipers... :thumbsup:)

The only way I can see that I am going to be able to secure it is with some spacing rings so I can screw everything up tight.

However, there is no 'shoulder' on the flattener to sit these spacing rings against - the threads just sort of stop.

Has anyone faced this issue before and found a solution?

Cheers
Adam

[naskies]

Hi all,

I'm trying to figure out the exact part numbers I need to hook up my FS-60CB + flattener to my Canon DSLRs. I'm still confused after reading through this thread...

I see that there is a Takahashi Wide Mount T-Ring for Canon EOS Cameras (http://www.optcorp.com/product.aspx?pid=7424&kw=takahashi%20wide%20mount%20ring&st=2) that looks like it will attach directly onto the Canon EOS bayonet, as well as a Takahashi Wide Mount Ring to FS-60C for Canon EOS (http://www.optcorp.com/product.aspx?pid=15678&kw=takahashi%20wide%20mount%20ring&st=2) - but this one doesn't have the Canon EOS bayonet (identical to the photos in Adam's first post in this thread).

I see that there is a Takahashi Wide Mount - T-Ring Only (http://www.optcorp.com/product.aspx?pid=3500&kw=takahashi%20wide%20mount%20ring&st=2) available too.

Any suggestions on the exact parts (and part numbers) that I'll need? The Tak system guide manuals for the FS-60CB/Q were no help. I'd also like to get the Nikon mounting rings too - I don't have one, but many of my friends do :)

Thanks everyone!

Dave

[naskies]

I went ahead and ordered the FS-60CB specific wide T-mounts for Canon from Peter Tan. It came with a standard Canon EOS T-ring adapter plus two different sizes of the adapter shown in Adam's first post of this thread. Thanks to Peter's post, I managed to figure out what had to be swapped around.

The whole set up (FS-60CB + adapter + CAA + SD ring + flattener + wide T-mount + Canon 5DmkII) works, but I'm getting really bad field curvature in the corners - as per Adam's later posts.

Any suggestions on how to get the flattener-camera spacing exactly right?

[naskies]

Ah-ha! It looks like I was shipped the wrong T-ring (despite my care in specifying the part from the system guide), so the flattener doesn't connect to the camera as in this picture from the Tak website.

I was connecting the Canon EOS adapter directly to the flattener without the bit in between... hence the spacing was off.

[RickS]

Good bit of detective work, Dave :thumbsup: Tak don't make it easy...