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Any issue with replacing a 10” (254mm) f/5 with 250mm f/5?

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6 replies to this topic

#1 Sassenach

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Posted 28 November 2021 - 05:48 PM

Dear all,

i am looking into replacing my primary mirror. My current mirror is 10” = 254mm with f/5 = 1270mm.

 

Since I live in Europe, it is easier to find 250mm primary mirrors. I have found a 255mm mirror from Astroreflect, but waiting time is 9 months.

 

Are there any issues with swapping in a 250mm f/5 I should know about? This would be 1250mm focal length so 20mm shorter than my current setup on my 10” Bresser Messier.

 

thanks!


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#2 PrestonE

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Posted 28 November 2021 - 06:08 PM

I do not see any problem...

 

Though your focuser may not have enough

In Travel to reach focus...

 

Just depends on how it is currently set up...

 

Regards,

 

Preston



#3 Tangerman

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Posted 28 November 2021 - 06:42 PM

You should measure the actual focal length of your current primary mirror. If it's actually closer to 1250 mm than 1270, this would be even easier. But you may need to move your mirror up a little bit or get a low-profile focuser, depending on the current focal length and where your eyepieces currently reach focus. Neither of which should be too difficult. 



#4 Pinbout

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Posted 28 November 2021 - 09:22 PM

<You should measure the actual focal length of your current primary mirror.>

 

measure the RoC with a knife edge on the “bench” then divide by 2 for focal length 

 

https://youtu.be/wKm1SIJBR1E



#5 javad

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Posted 29 November 2021 - 02:44 AM

Dear all,
i am looking into replacing my primary mirror. My current mirror is 10” = 254mm with f/5 = 1270mm.

Since I live in Europe, it is easier to find 250mm primary mirrors. I have found a 255mm mirror from Astroreflect, but waiting time is 9 months.

Are there any issues with swapping in a 250mm f/5 I should know about? This would be 1250mm focal length so 20mm shorter than my current setup on my 10” Bresser Messier.

thanks!



I am also looking around for such mirrors. There is also TS branded mirrors, do you have any info about them? But yes, AstroReflect ones are slimmer and lighter.

#6 PETER DREW

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Posted 29 November 2021 - 04:04 PM

Measuring diameters and focal lengths is important, few mirrors are exactly as quoted.


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#7 Dan_I

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Posted 30 November 2021 - 02:45 PM

Dear all,

i am looking into replacing my primary mirror. My current mirror is 10” = 254mm with f/5 = 1270mm.

 

Since I live in Europe, it is easier to find 250mm primary mirrors. I have found a 255mm mirror from Astroreflect, but waiting time is 9 months.

 

Are there any issues with swapping in a 250mm f/5 I should know about? This would be 1250mm focal length so 20mm shorter than my current setup on my 10” Bresser Messier.

 

thanks!

Romano Zen in Venice can make one for you in less than two months (and of very good quality).




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