Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

8" f/6 or 8" f/7

This topic has been archived. This means that you cannot reply to this topic.
6 replies to this topic

#1 Guest_**DONOTDELETE**_*

Guest_**DONOTDELETE**_*
  • -----
  • topic starter

Posted 07 February 2004 - 06:07 PM

Hey guys,

I'm still considering buying an 8" DHQ either f/6 or f/7. Which would you reccomend? This will be my first scope, and I realize that f/7 is better for planets than the f/6 and that the f/6 has a wider field of view, but I'm not sure which to choose. Also, I can switch the focuser for a Crayford; Is the Crayford focuser worth the extra bucks($60)? Also, should I get a Telrad instead of the 6x30 finder. The Telrad would cost an extra $10. Or should I get a 7x50 for an extra $45?

Thanks

#2 Tom L

Tom L

    ISS

  • *****
  • Posts: 31,061
  • Joined: 07 Jan 2004

Posted 07 February 2004 - 06:15 PM

F/7, Yes, yes, YES!!! Get the Telrad. IF I had a choice between the f/6 and f/7 (I have a f/6 and love the scope), I would get the longer because it reduces the burden on the eyepieces to be "better". What I mean is that an average eyepiece will perform a little better in a slower scope.



#3 Relativist

Relativist

    Cosmos

  • *****
  • Posts: 8,161
  • Joined: 11 Oct 2003

Posted 08 February 2004 - 01:22 AM

Just make sure it fits in your car, and make sure that you absolutely can't handle a 10"

.........Curtis

#4 lighttrap

lighttrap

    Soyuz

  • *****
  • Posts: 3,833
  • Joined: 06 Feb 2004

Posted 08 February 2004 - 11:08 AM

Johnny,
Take this for what it's worth. (Arguably not much.)
I've got a 6" Discovery f/5 and a Hardin DSH 8" f/6, and I think that the build quality on the Guan Sheng Hardin 8" is MUCH better than on the Discovery DHQ. I also think it's a much better value. The reasons I say that are that the Tiawanese GS "Hardin" (sold as several other brands) has:

-metal tube instead of sonotube
-tension springs to make the tube captive to the mount, (unlike the Discovery which relies solely on gravity to rest in the cradle
-is therefore easier to carry as a single unit)
-came with a 50mm finder
-seems to actually have a better mirror (maybe, possibly, hard to say when comparing different focal lengths

That gets me to your orig. question: f/6 vs f/7? If all else was equal, I'd go with the f/7. But, all else is rarely equal. Would I go for an f/7 Discovery or an f/6 Hardin? Well, in reality, when it came time to actually make the call, I went with the Hardin. But, that's just me. I wish more of these mid-sized scopes came with f/7 as an option, since it's a nice compromise between f/6 & f/8. But, even at f/6, it's slow enough to get good service out of relatively cheap eyepieces, (unlike f/4 & f/5).

The Discovery would probably have a slightly higher resale value sometime down the road, if that's at all important to you.

Just one guy's biased opinions. Take with salt.
Mike Swaim

#5 jmoore

jmoore

    Surveyor 1

  • *****
  • Posts: 1,959
  • Joined: 01 Oct 2003

Posted 08 February 2004 - 12:21 PM

I'd vote f/7.

Negative: narrower FOV, but it won't be THAT much narrower (for example, w/ 32mm EP, 1.2 deg in f7 vs. 1.4 deg in the f6).

Positive: better EP performance, and less-sensitive to precise collimation

If I was using an equatorial mount, I might lean toward f6 because it's smaller and thus a little easier to deal with. But for a Dob, I agree with everyone else...longer is better...(I'm still talking about the telescope, of course).

jeff

#6 Guest_**DONOTDELETE**_*

Guest_**DONOTDELETE**_*
  • -----
  • topic starter

Posted 08 February 2004 - 01:13 PM

Thanks guys. I'll probaly get the DHQ f/7, but the PDHQ 8" f/7 is tempting for $799. Do yall know if the PDHQ would be worth the extra $$$?

#7 litespeed

litespeed

    Viking 1

  • -----
  • Posts: 984
  • Joined: 31 Oct 2003

Posted 08 February 2004 - 04:23 PM

John,

The difference in those two sets of optics is fairly substantial. The Premium mirror offers 94% ref. versus 89% for the standard. The premium also uses pyrex glass versus the sodium lime. There are plenty of other differences too. But I think most of those questions should be addressed in the optical forum and addressed to "AlM". He can give you a very specific answer.

I was actually considering one of there 10" mirrors for my project scope.


AJ



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics