Question: Quality of "Digital Optics" Lenses

[Guest]

Archived from groups: rec.photo.digital (More info?)

In message <NfadnVMd5Z1f70DfRVn-hg@comcast.com>,
"Nostrobino" <not@home.today> wrote:

>"wilt" <wiltw@aol.com> wrote in message
>news:1121805441.190331.54990@o13g2000cwo.googlegroups.com...
>> "2X telephoto...900mm effective" You are quite confused, it sounds.
>> In order for 2X to provide 900mm effective, you have to start with
>> 450mm!!! Put it in front of 80mm, and you end up with something
>> similar to a 160mm lens.
>
>Where'd you get that 80mm, though? He's asking about putting the 2x
>converter on a 75-300mm lens. Given the Canon's 1.6x focal length factor,
>that works out to 960mm effective equivalent.

.... but what does that mean, in practical terms? Nothing, because a
sharp 300mm lens will capture more subject detail from the same distance
as this combo will.

--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 

[Guest]

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<JPS@no.komm> wrote in message
news:3fuqd1tbf89njuem4q35bbnkfuhh8irpf2@4ax.com...
> In message <NfadnVMd5Z1f70DfRVn-hg@comcast.com>,
> "Nostrobino" <not@home.today> wrote:
>
>>"wilt" <wiltw@aol.com> wrote in message
>>news:1121805441.190331.54990@o13g2000cwo.googlegroups.com...
>>> "2X telephoto...900mm effective" You are quite confused, it sounds.
>>> In order for 2X to provide 900mm effective, you have to start with
>>> 450mm!!! Put it in front of 80mm, and you end up with something
>>> similar to a 160mm lens.
>>
>>Where'd you get that 80mm, though? He's asking about putting the 2x
>>converter on a 75-300mm lens. Given the Canon's 1.6x focal length factor,
>>that works out to 960mm effective equivalent.
>
> ... but what does that mean, in practical terms? Nothing, because a
> sharp 300mm lens will capture more subject detail from the same distance
> as this combo will.

Probably. I think it's moot anyway, since I doubt it's practical to put an
inexpensive 2x front-end converter on a 75-300mm lens.

N.

 

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"wilt" <wiltw@aol.com> wrote in message
news:1121812617.933936.301340@o13g2000cwo.googlegroups.com...
> <<Where'd you get that 80mm, though? He's asking about putting the 2x
> converter on a 75-300mm lens. Given the Canon's 1.6x focal length
> factor,
> that works out to 960mm effective equivalent.>>
>
> The original post did not say '960mm equivalent field of view'...it
> simply said 2X on 300mm, and that is 600mm according to how I was
> taught multiplication.

When you were taught multiplication, did they teach you to just insert the
number 80 randomly into the problem? As I asked, "where'd you get that
80mm"? No one else had mentioned anything about "80mm"; it appears to be
something you just pulled out of the blue.

The OP clearly knows that Canon dSLR has a 1.6 focal length factor for the
35mm equivalence which almost everyone understands and relates to. That's
where he got the ~900mm (actually 960mm if all the numbers were precisely
correct, which is unlikely) for the combination.

N.

 

[Guest]

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JPS@no.komm <JPS@no.komm> wrote:
>
> Well, that depends on your budget. If price is not an issue, skip the
> 75-300, as it will probably become redundant when you decide to get a
> better lens.

.... unless you go on long (multi-day) hikes, in which case you'll want
the lightest telephoto lens you can find, and the 75-300 is it.

I'm still looking at the Sigma 80-400 to replace my 75-300 for primary
telephoto use, but I'd never try to drag that much weight into the
mountains.

--
Zed Pobre <zed@resonant.org> a.k.a. Zed Pobre <zed@debian.org>
PGP key and fingerprint available on finger; encrypted mail welcomed.

 

[carlos]

Archived from groups: rec.photo.digital (More info?)

Hi.
I have a 75-300 IS and it suites me fine. It's not a series L lens but
have a excellent image that my money can give. ;-)

If you intend to use a 2x teleconverter, so, forget the 75-300. You are
using a Canon and I recommend that you use a canon TC too, but the
problem is: Neither the 2x TC and 1.4X TC can be mounted on the 75-300.
These TC´s accepts only some series L lens.


BD wrote:
> Hi, all.
>
> I'm looking at options for my new Rebel 300d.
>
> I am considering Canon's 75-300 IS lens. I expect it would be a good
> choice.
>
> I see an inexpensive 2x telephoto out there, from a company called
> Digital Optics. this would give me 900mm effective (yikes!).
>
> Does anyone know about this crew's lenses? It's certainly a low price
> point ($60 for the 2x), so I am suspicious of the quality. On the other
> hand, it's cheap enough that it might just be worth getting for kicks.
>
> But some precedent on Digital Optics' quality would be useful.
>
> Any wisdom out there?
>
> Thanks!
>
> DW.
>

--
gutto@iis.com.br

Carlos A. B. Coutinho
Rio de Janeiro, RJ
Brasil

 

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"BD" <bobby_dread@hotmail.com> wrote in message
news:1121798518.376446.71680@o13g2000cwo.googlegroups.com...
> Hi, all.
>
> I'm looking at options for my new Rebel 300d.
>
> I am considering Canon's 75-300 IS lens. I expect it would be a good
> choice.
>
> I see an inexpensive 2x telephoto out there, from a company called
> Digital Optics. this would give me 900mm effective (yikes!).
>
> Does anyone know about this crew's lenses? It's certainly a low price
> point ($60 for the 2x), so I am suspicious of the quality. On the other
> hand, it's cheap enough that it might just be worth getting for kicks.
>
> But some precedent on Digital Optics' quality would be useful.
>
> Any wisdom out there?
>
> Thanks!
>
> DW.
>
BD, You mentioned astro photography in one of your replies in this thread.
In this case, I would forget about the 75-300 and save for a 300mm f/4 L IS
and a 1.4 or 2x converter. After trying the zooms, I ended up getting the L
glass. That 300mm is a great way to enter Canon's telephoto L glass series.
Here is a couple of examples with Canon's 2x converter attached:
http://home.att.net/~jriegle/moon.jpg

http://home.att.net/~jriegle/grackle1.jpg

John

 

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In article <1121810905.678442.160390@g44g2000cwa.googlegroups.com>,
"BD" <bobby_dread@hotmail.com> wrote:

> Really?! Can you email me offline and let me know what you'd want for
> it? Perhaps also a shipping estimate to the Vancouver area?

Oh, no, sorry. I can't ship to my friends up north!

It is an excellent lens though.

--

http://home.nc.rr.com/christianbonanno/

 

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Nostrobino wrote:
>
> "BD" <bobby_dread@hotmail.com> wrote in message
> news:1121805923.443417.126080@z14g2000cwz.googlegroups.com...
> >I will admit to being confused, as I'm only starting to get my head
> > around the vernacular. the 900 effective comes from:
> >
> > Native lens length = 300
> > Teleconverter = 2x => 600mm
> > x 1.6 to 'translate' from 35mm to digicam equivalent => ~900mm.
>
> Yes, close enough. It works out to 960mm of course, but none of these
> numbers are likely to be exactly as advertised anyway.
>
> >
> > I'm not intentionally talking out of my arse or being obtuse, I'm just
> > at the start of a bit of a learning curve.
>
> You're doing okay. But I think once you deal with an 480mm equivalent or
> thereabouts, you probably will find that more than enough of a handful.
>
> I can understand your being interested in photographing the moon. The
> problem there is that the moon's been photographed 18,745,904,320,417 times
> already, with several million of those being done with equipment you cannot
> possibly begin to compete with. I would just buy a book with some good moon
> photographs, of which there must be many. ;-)
>
> Even a 960mm (equivalent) lens is not going to fill the frame with the moon
> very well. The moon's about 2,000 miles in diameter and what, 238,000 miles
> away? So with a 960mm lens on a 35 the moon image would be 2 / 238 * 960 =
> 8.07 mm diameter, or about one-third the height of the frame. If you take a
> long-lens shot and magnify the moon with software you'll probably do about
> as well as you'd do with a cheap 2x converter (if you could even get one on
> that lens in the first place).
>
> N.

The *actual* focal length of the combo is 600mm, not 960. 960 is the
35mm equivalent, not actual. The image size is independent of any
sensor, so it will be 2/238*600 = 5.04 mm, about a third of the 300D
sensor size.

Colin

 

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"Colin D" <ColinD@killspam.127.0.0.1> wrote in message
news:42DD9B5E.57734A81@killspam.127.0.0.1...
>
>
> Nostrobino wrote:
>>
>> "BD" <bobby_dread@hotmail.com> wrote in message
>> news:1121805923.443417.126080@z14g2000cwz.googlegroups.com...
>> >I will admit to being confused, as I'm only starting to get my head
>> > around the vernacular. the 900 effective comes from:
>> >
>> > Native lens length = 300
>> > Teleconverter = 2x => 600mm
>> > x 1.6 to 'translate' from 35mm to digicam equivalent => ~900mm.
>>
>> Yes, close enough. It works out to 960mm of course, but none of these
>> numbers are likely to be exactly as advertised anyway.
>>
>> >
>> > I'm not intentionally talking out of my arse or being obtuse, I'm just
>> > at the start of a bit of a learning curve.
>>
>> You're doing okay. But I think once you deal with an 480mm equivalent or
>> thereabouts, you probably will find that more than enough of a handful.
>>
>> I can understand your being interested in photographing the moon. The
>> problem there is that the moon's been photographed 18,745,904,320,417
>> times
>> already, with several million of those being done with equipment you
>> cannot
>> possibly begin to compete with. I would just buy a book with some good
>> moon
>> photographs, of which there must be many. ;-)
>>
>> Even a 960mm (equivalent) lens is not going to fill the frame with the
>> moon
>> very well. The moon's about 2,000 miles in diameter and what, 238,000
>> miles
>> away? So with a 960mm lens on a 35 the moon image would be 2 / 238 * 960
>> =
>> 8.07 mm diameter, or about one-third the height of the frame. If you take
>> a
>> long-lens shot and magnify the moon with software you'll probably do
>> about
>> as well as you'd do with a cheap 2x converter (if you could even get one
>> on
>> that lens in the first place).
>>
>> N.
>
> The *actual* focal length of the combo is 600mm, not 960. 960 is the
> 35mm equivalent, not actual.

Which is exactly what I said it was:
>> Even a 960mm (equivalent) lens [etc., etc.]

I think everyone understands what "(equivalent)" means in this context.


> The image size is independent of any
> sensor, so it will be 2/238*600 = 5.04 mm, about a third of the 300D
> sensor size.

The salient point is that it *is* about a third of the frame height,
whichever way you look at it. As I said,
>> So with a 960mm lens on a 35 the moon image would be 2 / 238 * 960 =
>> 8.07 mm diameter, or about one-third the height of the frame.

Change that to the actual focal length and sensor dimensions and the result
is the same, it's still about a third of the frame height.

The OP was using the 35mm equivalencies which are familiar to most of us,
and I continued the same usage.

N.