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09-26-2011, 08:48 PM   #1
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645 FA300/4 distance scale off?

Recently I found its distance scale is not right. When I AF to infinity, it shows a little over 30m mark. When I MF to infinity mark, infinity object is not clear in viewfinder. I could MF slightly over infinity mark. But the other end is under 3m quite a bit. And when compared with other 645 lenses, I could tell the distance scale on my FA300 is wrong (not accurate).

I can still AF it to get sharp image in viewfinder. MF seems smooth too.

But what's wrong with the distance scale and the two focus ends with this lens? Anyone has similar experience?

Thanks a lot!


Last edited by hyyz; 09-27-2011 at 07:23 AM.
09-26-2011, 08:54 PM   #2
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I don't have this lens or even 645, but it's normal for long teles to focus past infinity. However, the scale should match the actual focus because it's part of the design. The good news is adjusting the actual focus to match the scale is relatively easy for any service centres.
09-26-2011, 11:22 PM   #3
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QuoteOriginally posted by wlachan Quote
I don't have this lens or even 645, but it's normal for long teles to focus past infinity.
Correct, this is because temperature often causes the metal the lens is made of to expand and shrink they deliberately compensate for this effect by making the lens able to focus nearer and further than it is supposed to - which is supposedly why canon lenses are the off white colour they are, because it is said to reflect heat and control the temperature of the lens.
09-27-2011, 07:23 AM   #4
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Thanks both of you for the explanation. I will probably send it to Pentax for calibration. Any idea about the cost?

09-27-2011, 01:51 PM   #5
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By infinity, you mean something like the moon? This far away are not at infinity.

Why send it to Pentax--your AF is working and you can focus in the viewfinder. How is the scale accuracy going to be useful?
09-27-2011, 09:13 PM   #6
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I probably don't have to send for service. I'm just not sure if what I observed is a sign that something else is failing.

It would be great if someone else also has the experience and can give me advice on whether it will worsen overtime.

Thanks for the insight.
09-28-2011, 04:26 AM   #7
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QuoteOriginally posted by hyyz Quote
... give me advice on whether it will worsen overtime.
Unlikely - I have a Pentax 645 A*600mm f/5.6 and Pentax 67 M*800mm f/6.7 that exhibit exactly the same characteristic, it is perfectly normal.
09-28-2011, 07:46 AM   #8
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QuoteOriginally posted by Digitalis Quote
Unlikely - I have a Pentax 645 A*600mm f/5.6 and Pentax 67 M*800mm f/6.7 that exhibit exactly the same characteristic, it is perfectly normal.
Good to know it is normal. This makes me feel better. Thank you for the advice!

I just decide to shoot a roll with this lens now that fall is coming

09-28-2011, 12:13 PM   #9
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QuoteOriginally posted by hyyz Quote
I probably don't have to send for service. I'm just not sure if what I observed is a sign that something else is failing.

It would be great if someone else also has the experience and can give me advice on whether it will worsen overtime.

Thanks for the insight.
My experience with the 645FA300, 67M*400 (plus other long/super teles) is the distance scale is only a rough indication due to the size of these optic and thermal expansion/contraction.

I would only be concern of need for servicing when I am absolutely sure that the focus screen is in focus or AF is functioning and the resulting image has focus issues. I say absolutely meaning checking one's vision/eyesight as well; it is part of the chain that needs to all function properly to ensure focus.
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