Esprit 80 spacing distance

[newbie alert]

Hi Guys, just going around in circles here..

I purchased a second-hand esprit 80 a few months back where the guy said the spacing was 65mm, I've looked in a few places now where the spacing differs from 75mm down to 55mm with most figures in between.. Skywatchers manual says 66mm but that's incorporating the removal of the 6mm adapter to allow extra backfocus should it be needed..

I read something on I think was on cloudy nights where someone says if you take the 6mm spacer off it's 66mm and leave it off it's 61 which don't add up unless a 6 mm spacer is 5mm? 

I'm at a loss, I initially put it at 65 as the previous owner says, then I read it should be 55mm so changed it again, I 've also had the same issues with atik as their manual says the sensor is "approx 18mm"

If you look at it it's not looking that far back so I think it's 15mm..

I'm thinking if I shine a torch down the front, remove the camera and filter wheel and see where the light comes to point of focus, would that work?

[Adam J]

5 minutes ago, newbie alert said:

Hi Guys, just going around in circles here..

I purchased a second-hand esprit 80 a few months back where the guy said the spacing was 65mm, I've looked in a few places now where the spacing differs from 75mm down to 55mm with most figures in between.. Skywatchers manual says 66mm but that's incorporating the removal of the 6mm adapter to allow extra backfocus should it be needed..

I read something on I think was on cloudy nights where someone says if you take the 6mm spacer off it's 66mm and leave it off it's 61 which don't add up unless a 6 mm spacer is 5mm? 

I'm at a loss, I initially put it at 65 as the previous owner says, then I read it should be 55mm so changed it again, I 've also had the same issues with atik as their manual says the sensor is "approx 18mm"

If you look at it it's not looking that far back so I think it's 15mm..

I'm thinking if I shine a torch down the front, remove the camera and filter wheel and see where the light comes to point of focus, would that work?

my understanding is that with the space on the flattner its 55mm back focus. Could be wrong though.

[Jkulin]

From the shoulder of the flattener to the CCD is 55mm, get it as close to this as possible or you'll end up with odd shaped stars.

[newbie alert]

Thanks guys, but I'm at 56mm( 1mm for filters thickness) at the moment, stars look nice and round at all distances that I've tried with the luminance  although I've not just yet taken an image with it..

I'm using Artemis capture ,and the only thing I've changed is the filter wheel and lrgb,  the HA is the same..can't see a star in a 30- 60 sec sub with the HA filter for focus..it's not going to be too far away from the luminance even if they're not parfocal

Here's some darks just taken and shows roughly the same as pointing at the sky..to get a star to show on the screen I have to adjust the log in the -7 range..I used to use -1 and even then I need to have some white showing by adjusting the white point slider 

[Adam J]

Accounting for filters is going to be interesting when I get mine, I have baader LRGB at 2mm thickness and astrodon narrowband at 3mm thickness but am hoping that is i tube it to the astrodons the 0.3mm difference in licght path wont make any difference for the baaders. 

[Anthonyexmouth]

2 hours ago, newbie alert said:

Hi Guys, just going around in circles here..

I purchased a second-hand esprit 80 a few months back where the guy said the spacing was 65mm, I've looked in a few places now where the spacing differs from 75mm down to 55mm with most figures in between.. Skywatchers manual says 66mm but that's incorporating the removal of the 6mm adapter to allow extra backfocus should it be needed..

I read something on I think was on cloudy nights where someone says if you take the 6mm spacer off it's 66mm and leave it off it's 61 which don't add up unless a 6 mm spacer is 5mm? 

I'm at a loss, I initially put it at 65 as the previous owner says, then I read it should be 55mm so changed it again, I 've also had the same issues with atik as their manual says the sensor is "approx 18mm"

If you look at it it's not looking that far back so I think it's 15mm..

I'm thinking if I shine a torch down the front, remove the camera and filter wheel and see where the light comes to point of focus, would that work?

What camera and what flattener are you using?

[newbie alert]

48 minutes ago, Anthonyexmouth said:

What camera and what flattener are you using?

It's an old atik 16hr,  flattener is the esprit one

[Adam J]

On 03/10/2019 at 13:05, newbie alert said:

It's an old atik 16hr,  flattener is the esprit one

That's a small sensor it's very unlikely to be crytical. 

[newbie alert]

2 hours ago, Adam J said:

That's a small sensor it's very unlikely to be crytical. 

Enough to make it not see any stars in HA 

[Adam J]

41 minutes ago, newbie alert said:

Enough to make it not see any stars in HA 

Your saying that you cant see any stars on a Ha image and that you think that is caused but the spacing?

I very much doubt that is the case, you should be seeing stars even if its way off.

Adam

[newbie alert]

4 minutes ago, Adam J said:

Your saying that you cant see any stars on a Ha image and that you think that is caused but the spacing?

I very much doubt that is the case, you should be seeing stars even if its way off.

Adam

Initially I thought I had the filters back to front so I had a quick search and it says there's no direction..could it be this?

[Adam J]

12 minutes ago, newbie alert said:

Initially I thought I had the filters back to front so I had a quick search and it says there's no direction..could it be this?

No it wont be that, they will work in either direction in terms of filtering, but it is worth noting that there is a correct direction for anti reflection coating.

[newbie alert]

Any more ideas?

I did a rough test to see where the focus point was and yes it's at 55mm as far as I could tell

[Jkulin]

19 hours ago, Adam J said:

No it wont be that, they will work in either direction in terms of filtering, but it is worth noting that there is a correct direction for anti reflection coating.

There might be with some filters Adam, but when I asked the question from Chroma as some are not marked, they said it made no odds whatsoever with their filters, not sure about other brands though.

[newbie alert]

4 hours ago, Jkulin said:

There might be with some filters Adam, but when I asked the question from Chroma as some are not marked, they said it made no odds whatsoever with their filters, not sure about other brands though.

Had a bit more search time and it seems that there wouldn't be a problem with it either way around other than if there was light leakage into the filter wheel and it might cause reflective issues..which isn't the cause in this case