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Esprit 120 Imaging Rig - focuser in-focus position quite far out


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13 hours ago, gilesco said:

I am not trying to change how far back my sensor is.

Perhaps this (it is an exaggerated scale) will make it more clear. When the tube is extended further there is more sag (upper image of focuser tube and draw tube):

image.thumb.png.73c2337caa7706609550d725d9f44c5d.png

If the tube achieves focus without being as extended as much (lower image) there is less sag.

Of course the lower image means the camera is closer, and so spacers are required to the right of the drawtube to compensate for that distance.

In any case, as others have noted- and this is an exaggerated scale, the Esprit focuser is a very snug fit and others don't expect this issue. But if you had a cheaper not so snug focuser, it would be an issue.

Hi..  It’s not quite like that as the focuser bearings are a fixed length     and so support the same length of drawtube regardless of how far it is extended 

Dave

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9 minutes ago, Laurin Dave said:

its both 63 and 55 mm ..   the flattener has an 8mm spacer/ adapter attached that reduces the thread from M66 to M48..   on the 150 there’s a somewhat longer M62 to M48 spacer .(I think the 120 is the same as the 150)    So for the 100 it’s 63mm if your using the M66 thread and 55mm if using the  M48 thread ..  

The initial result I've got from the 120 tell me that backfocus is just spot on with the FLO supplied adapter for CMOS cameras.

I had heard about the manual errors, back focus worries before purchase etc ... but FLO supplied everything to make it work! No extra stuff needed, will probably post an instance of my first image, from a single bad seeing session shortly.

Edited by gilesco
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9 minutes ago, gilesco said:

The initial result I've got from the 120 tell me that backfocus is just spot on with the FLO supplied adapter for CMOS cameras.

I had heard about the manual errors, back focus worries before purchase etc ... but FLO supplied everything to make it work! No extra stuff needed, will probably post an instance of my first image, from a single bad seeing session shortly.

Excellent. Looking forward to seeing it .  as I’m sure you’ve got, it’s 55mm from the m48 thread , also at f7 pretty forgiving and with a smallish  sensor (Sony694 size) I’m told by a ‘man who knows’ that you can dispense with the flattener 

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So this is the only image I have made with the Esprit 120. I am happy with it, it is my first image with it, I am not complaining about it, there is a lot in there that is an imperfection of my own processing etc... I only started this thread with a concern about having the "in-focus" position at an outer point in the total focuser walk.

 

1812293808_PinwheelGalaxy2020-12-07.thumb.jpg.94d31b8d8c3b363160d05521e9711a67.jpg

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Hi Giles,

I have an Esprit 150ED and the same 'issue' as you have. So far I did not experience that the long extension of the focuser was an issue for its stability. Still I feared that, as you wrote, that the extended focuser could be (or become) an issue, while for those rare occasions that I wanted to do visual observing I really needed an extension. So I made one myself on my lathe from aluminium tube which adds 45mm to the focuser, and had it spray painted white (together with my GTT60 that sits next to it) to fit the main OTA. You can see the before (all is black) and after (white section in between) situations in below images. Now I am focusing at around 15mm on the focuser scale.

Nicolàs

DSCN2670e.JPG

DSCN3401e.JPG

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On 16/12/2020 at 20:34, gilesco said:

Can't help but notice you have a Pegasus attached there, how did you go about that?

(I'm choosing to mount it on something attached to the tube rings).

Hello

its literally on some Velcro, which I was skeptical about, but I’ve used some incredible strong stuff. It doesn’t budge and is quite difficult to actually remove the box it’s that hooked on

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On 16/12/2020 at 07:51, gilesco said:

I am not trying to change how far back my sensor is.

Perhaps this (it is an exaggerated scale) will make it more clear. When the tube is extended further there is more sag (upper image of focuser tube and draw tube):

image.thumb.png.73c2337caa7706609550d725d9f44c5d.png

If the tube achieves focus without being as extended as much (lower image) there is less sag.

Of course the lower image means the camera is closer, and so spacers are required to the right of the drawtube to compensate for that distance.

In any case, as others have noted- and this is an exaggerated scale, the Esprit focuser is a very snug fit and others don't expect this issue. But if you had a cheaper not so snug focuser, it would be an issue.

The focuser does not work like you show in the diagram. The same length of tube is in contact with the pads and linear bearing irrespective of the amount of travel. 

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  • 4 weeks later...

Hi guys, this is my first post ever on this website. I got an Esprit 120 used with a Feather Touch focuser. Its drawtube is not long enough at all, so it came with a spacer. However, the spacer's threads aren't great and are the cause of some slight tilt. Do you think adding a 0.75x reducer/flattener will fix the issues with our focusing distance? I figured this thought might be useful for you guys as well as me.

Jaxon

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15 minutes ago, Jt_3232 said:

Hi guys, this is my first post ever on this website. I got an Esprit 120 used with a Feather Touch focuser. Its drawtube is not long enough at all, so it came with a spacer. However, the spacer's threads aren't great and are the cause of some slight tilt. Do you think adding a 0.75x reducer/flattener will fix the issues with our focusing distance? I figured this thought might be useful for you guys as well as me.

Jaxon

Does your scope have a Riser between the Adapter and the Focuser? Have a look on the Starlight Instruments website to see what these are ..  the Riser is basically a tube that puts the focuser at the correct distance ..  if you have the flattener this should screw onto the focuser draw tube direct (via what’s known as an End Cap)..  so the configuration would be scope..  adapter..  riser..  focuser..  end cap..  flattener..  spacers.. camera 

HTH

ps I don’t think the Skywatcher reducer will screw into the Starlight draw tube ..  

Edited by Laurin Dave
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Hi,

Thanks for the ultra great suggestion. Let me follow that up with a stupid question: how do I know if I have a 3" or 3.5" focused? I measured the diameter of the hole of the focuser, it is 3 inches. Does that make it a 3" focuser?

I have an end cap and it screws into the focuser and the flattener, so I am covered there. 

So I should get the riser for the 3" focuser? Would using a reducer/flattener change the inward focus enough that I don't need the riser?

Thanks!

Jaxon

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On 15/12/2020 at 13:29, arrayschism said:

Yep, mine's the same - haven't got a precise measurement of what it is as it's not to hand right now... but the drawtube is way out before focus. 75% sounds about right where mine is.

This means however that you have sufficient in focus to add accessories such as a filter wheel or ADC which require about 50 mm of in focus.

John 

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On 16/12/2020 at 20:34, gilesco said:

Can't help but notice you have a Pegasus attached there, how did you go about that?

(I'm choosing to mount it on something attached to the tube rings).

If you mount it on the dove tail I found it can actually rotate the scope in the rings if not perfectly aligned, as a result of causes guiding issues following autofocuser movements.

 

Hence I changed to mounting it using the outer two screws. Much better. 

Edited by Adam J
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  • 1 year later...
  • 3 months later...
On 14/12/2020 at 12:03, gilesco said:

So, I have the following imaging train attached to my Esprit 120:

Stock Focuser  --> 3" to M74 adapter --> 9mm Filter Cell Adapter --> Esprit 120 Field Corrector --> 20mm Spacer --> ZWO OAG --> ZWO Spacer --> ZWO Filter Wheel --> ZWO ASI1600MM.

image.thumb.png.a5fd031d73159e9f888f099094fecfe0.png

With a tape measure I can see that I have the 75mm backfocus needed on the Field Corrector, and my imaging is good.

I have only been out once so far and got good results, but I couldn't hope but notice that my "in-focus" position on the drawtube was at least 75% focus tube extended. It didn't seem to introduce a specific issue, but would rather the in-focus position be with the draw tube less extended.

I suppose that I could try and find either some M74x1mm or M65x1mm spacers to go somewhere between the Field Corrector and the Focuser, but these seem few and far between - anyone have their focus position that far out on the Esprit 120?

Is it an issue? Could it cause draw-tube sag?

Anyone recommend a spacer available in the UK

This is a dead thread not sure why it came up. 

Edited by Adam J
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  • 5 months later...
On 14/12/2020 at 12:03, gilesco said:

So, I have the following imaging train attached to my Esprit 120:

Stock Focuser  --> 3" to M74 adapter --> 9mm Filter Cell Adapter --> Esprit 120 Field Corrector --> 20mm Spacer --> ZWO OAG --> ZWO Spacer --> ZWO Filter Wheel --> ZWO ASI1600MM.

image.thumb.png.a5fd031d73159e9f888f099094fecfe0.png

With a tape measure I can see that I have the 75mm backfocus needed on the Field Corrector, and my imaging is good.

I have only been out once so far and got good results, but I couldn't hope but notice that my "in-focus" position on the drawtube was at least 75% focus tube extended. It didn't seem to introduce a specific issue, but would rather the in-focus position be with the draw tube less extended.

I suppose that I could try and find either some M74x1mm or M65x1mm spacers to go somewhere between the Field Corrector and the Focuser, but these seem few and far between - anyone have their focus position that far out on the Esprit 120?

Is it an issue? Could it cause draw-tube sag?

Anyone recommend a spacer available in the UK?

Old thread I know, but I have just seen this, and very cheap, for anyone still interested….👍🏻

https://www.aliexpress.com/item/1005004961144941.html?spm=a2g0o.productlist.main.57.209be28aYQ8wtO&algo_pvid=124a2929-b2c7-486e-9bf8-21a3c279fa4c&algo_exp_id=124a2929-b2c7-486e-9bf8-21a3c279fa4c-28&pdp_ext_f={"sku_id"%3A"12000031164638437"}&pdp_npi=2%40dis!GBP!10.23!10.23!!!!!%402122457116753412318337069d0666!12000031164638437!sea&curPageLogUid=gI2lTmcDnv6A

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